Ambulatory medical apparatus and method using a robust communication protocol

ABSTRACT

An implanted medical device (e.g. infusion pump) and external device communicate with one another via telemetry wherein messages are transmitted under a robust communication protocol. The communication protocol gives enhanced assurance concerning the integrity of messages that impact medical operations of the implantable device. Messages are transmitted using a multipart format that includes a preamble, a frame sync, a telemetry ID, data, and a validation code. The data portion of the message includes an op-code that dictates various other elements that form part of the message. The data portion may also include additional elements such as sequence numbers, bolus numbers, and duplicate data elements. A telemetry ID for the transmitting device may be implicitly embedded in the message as part of the validation code that is sent with the message and that must be pre-known by the receiver to confirm the integrity of the received message.

RELATED APPLICATIONS

[0001] This application claims the benefit of prior filed U.S.Provisional Patent Application No. 60/177,414; filed Jan. 21, 2000, byRonald J. Lebel, et al., and entitled “Medical Apparatus and MethodIncluding an Implantable Device and an External Communication Device”.The entirety of this provisional application is hereby incorporatedherein by this reference, including appendices filed therewith and anyreferences incorporated therein by reference, as if set forth in fullherein.

FIELD OF THE DISCLOSURE

[0002] This invention relates generally to ambulatory medical systemsthat include a medical device and a control device that communicate viatelemetry and more particularly to devices that exchange messages usinga robust telemetry protocol. Preferred embodiments relate to implantableinfusion pumps and external devices for communicating therewith.

BACKGROUND

[0003] Various ambulatory medical devices have been proposed and anumber of such devices are commercially available. These devicesinclude, for example, implantable infusion pumps, externally carriedinfusion pumps, implantable pacemakers, implantable defibrillators,implantable neural stimulators, implantable physiological sensors,externally carried physiologic sensors, and the like.

[0004] Numerous electronic devices exist that communicate with oneanother using electromagnetic radiation of various wavelengths and ofvarious formats. These electronic devices can act as sources ofinterference that can negatively impact other devices that also need tocommunicate via telemetry. This is particularly true when other devicesattempt to communicate using small signal strengths that are typicallyassociated with the limited power that is available to ambulatorymedical devices and most particular to ambulatory devices that areimplanted within the body of a patient.

[0005] As appropriate operation of medical devices may be critical tothose patients being treated using those devices, and as telemetrycommunications between medical devices and external controllers cangreatly enhance the convenience of using such devices, or even be anenabling necessity to the use of such devices (e.g. implantable deviceswith sophisticated functionality), the operation of such medical devicescan benefit significantly by use of telemetry systems and protocols thathave features/elements that lead to optimization of various attributes.Attributes of interest may vary with circumstance but some attributes ofgeneral interest include (1) flexibility in communicating the widevariety signals that may be useful to controlling and retrievinginformation from a sophisticated medical device, (2) robustness indistinguishing actual signals from noise, (3) robustness indistinguishing valid signals from corrupt signals, (4) robustness inascertaining when appropriate communication has occurred and whenadditional communication must be attempted, (5) a reasonable efficiencyin communication time, and/or (6) a reasonable efficiency in electricalpower consumption associated with conveying information over thetelemetry system.

[0006] For example, implantable infusion pumps are generally configuredto accept infusion commands from an external communication device via anRF telemetry system, or the like. These commands may be used, interalia, to set program variables that are in turn used in defining thequantity and/or timing that is used in supplying a drug to the patient.As the dispensing of appropriate amounts of the drug may be critical tothe patient's well being, it is desirable that a reliable andtrustworthy communication channel exist between the externalcommunication device and the implantable device so that messages fromthe external communication device requesting drug delivery are receivedwith integrity, confirmation of accurate reception acknowledged in arapid manner, and minimal electric power consumption occurring in theentire process of listening for a message, receiving the message, andtransmitting a response to the message that is appropriately received bythe external communication device.

[0007] Implantable medical devices typically operate by battery power.The batteries may or may not be rechargeable. Higher consumption ofpower from an implantable medical device containing non-rechargeablebatteries leads to a shortening of the usable life of the device and anassociated increased frequency of surgery, potential pain, recovery, andinconvenience. Higher consumption of power from an implantable medicaldevice containing rechargeable batteries leads to more frequent chargingperiods for the batteries and associated inconvenience and may lead toan overall shortening of the usable life of the device. As such, whetheror not an implantable medical device contains rechargeable batteries ornon-rechargeable batteries, it is desirable to lower the powerconsumption of the device. As telemetry reception and transmission arehighly energy consumptive, it is desirable to minimize the operationtime of telemetry reception and transmission modules. As such it isdesirable to ensure that message length is kept to a minimum and thatrepeated transmissions and attempted receptions of previously sent butunsuccessfully received messages be kept to a minimum.

[0008] A need exists in the field for improved telemetryfeatures/elements that tend to optimize each of the above notedattributes individually, with out consideration of the impact on otherattributes, or tend to simultaneously optimize groups of selectedattributes, or tend to provide a balance between various ones of theattributes.

SUMMARY OF THE INVENTION

[0009] It is a first object of certain aspects of the invention toenhance the ability to communicate a wide variety signals that areuseful in controlling and retrieving information from an ambulatorymedical device.

[0010] It is a second object of certain aspects of the invention toenhance the robustness of distinguishing actual signals from whenreceiving telemetry communications in an ambulatory medical system.

[0011] It is a third object of certain aspects of the invention toenhance the robustness of distinguishing valid signals corrupt signalswhen receiving telemetry communications in an ambulatory medical system.

[0012] It is a fourth object of certain aspects of the invention toenhance the robustness of ascertaining when appropriate communicationhas occurred and when additional communication must be attempted in anambulatory medical system.

[0013] It is a fifth object of certain aspects of the invention todecrease the time that is spent in transmitting and receiving messagesusing a telemetry system in an ambulatory medical system.

[0014] It is a sixth object of certain aspects of the invention todecrease the electrical power consumption associated with conveying agiven amount of information via telemetry in an ambulatory medicalsystem.

[0015] Other objects and advantages of various aspects of the inventionwill be apparent to those of skill in the art upon review of theteachings herein. The various aspects of the invention set forth belowas well as other aspects of the invention not specifically set forthbelow but ascertained from the teachings found herein, may address theabove noted objects or other objects ascertained from the teachingsherein individually or in various combinations. As such, it is intendedthat each aspect of the invention address at least one of the abovenoted objects or address some other object that will be apparent to oneof skill in the art from a review of the teachings herein. It is notintended that all, or even a portion of these objects, necessarily beaddressed by any single aspect of the invention even though that may bethe case with regard to some aspects.

[0016] A first aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least a portion of the messagestransmitted between the communication device and the medical device aretransmitted using a message structure that includes a preamble, atelemetry identifier, and data.

[0017] In a specific variation of the first aspect of the invention, theCD telemetry system sends messages to the MD telemetry system using amessage structure that comprises: (1) an MD preamble, (2) an MDtelemetry identifier, (3) MD data including an op-code, and (4) an MDvalidation code.

[0018] In another specific variation of the first aspect of theinvention, the MD telemetry system sends messages to the CD telemetrysystem using a message structure that comprises: (1) a CD preamble, (2)a CD telemetry identifier, (3) CD data including a CD op-code, and (4) aCD validation code.

[0019] A second aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least a portion of the messagessent between the communication device and the medical device aredirected to specific medical device, or a specific communication device,by inclusion of an MD identifier that identifies the medical device or aCD identifier that identifies the communication device.

[0020] A third aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the integrity of at least aportion of a message passed between the communication device and medicaldevice is confirmed by analysis of a predefined interrelation between atleast two portions of the message.

[0021] A fourth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least one of the medical deviceor the communication device acts as a sender to transmit a message tothe other of the communication device or the medical device, which isthe intended receiver of the message, wherein the message is sent with avalidation code that is derived in part from the content of the messageand in part from other information not explicitly transmitted in themessage, and wherein the other information is known in advance by thereceiver and is used by the receiver in determining that the message wasreceived without error.

[0022] A fifth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein a message is sent using one of apredefined plurality of preambles.

[0023] A sixth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the communication device has a CDtelemetry identifier and the medical device has a MD telemetryidentifier wherein the length of the CD telemetry and MD telemetryidentifiers are different.

[0024] A seventh aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the MD telemetry system isconfigured to perform a bit pattern recognition that allows a selectedlevel of fault tolerance in concluding that a selected portion of amessage matches an expected pattern to be received.

[0025] A eighth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least one of the MD telemetrysystem or the CD telemetry system is configured to establish bitsynchronization using bit information transmitted in a preamble portionof a message and uses a different pattern to establish synchronizationfor groups of bits.

[0026] An ninth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least one of the MD telemetrysystem or the CD telemetry system is configured to establish framesynchronization and to confirm that a message is intended specificallyfor the medical device or the communication device, respectively, byconfirming receipt of a predefined identifier.

[0027] An tenth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein selected messages sent between theMD telemetry system and the CD telemetry system comprise characterpatterns that are incremented in relationship to corresponding characterpatterns included in one or more previous messages.

[0028] In a specific variation of the tenth aspect of the invention, thecharacter patterns are sequence numbers that are varied between firstand second messages that are varied within a receiver when they aresuccessfully received and varied within a transmitter when thetransmitter receives confirmation that the message was successfullyreceived.

[0029] A eleventh aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the communication device requirespre-knowledge of a telemetry identifier for the medical device prior tosending any messages to the medical device that can be used by themedical device to significantly modify the medical functioning of themedical device, or wherein the medical device requires pre-knowledge ofa telemetry identifier for the communication device prior to the medicaldevice accepting any messages from the communication device that can beused by the medical device to significantly modify the medicalfunctioning of the medical device.

[0030] A twelfth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system; and (c) a second device (SD) including atleast one infrared SD communication system, wherein the and CD telemetrysystem and the MD telemetry system are RF telemetry systems, and whereinthe communication device further comprises an infrared CD communicationsystem for sending messages to or receiving messages from the SDcommunication system.

[0031] A thirteenth aspect of the invention provides a medical systemthat includes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein a message is sent by thecommunication device to the medical device using a first framesynchronization pattern and wherein a message sent by the medical deviceto the communication device is sent with a second frame synchronizationpattern which is different from the first pattern.

[0032] Additional specific variations, provide the medical devices ofeach of the above aspects and above noted variations as implantabledevices such as implantable infusion pumps, implantable physiologicalsensors, implantable stimulators, and the like, or external devices suchas subcutaneous delivery infusion pumps or sensors that ascertain aphysiological parameter or parameters from subcutaneous tissue or fromthe skin of the patient. Such infusion pumps may dispense insulin,analgesics, neurological drugs, drugs for treating AIDS, drugs fortreating chronic ailments or acute ailments. Sensors may be used todetect various physiological parameters such as hormone levels, insulin,pH, oxygen, other blood chemical constituent levels, and the like. Thesensor may be of the electrochemical type, optical type, and may or maynot be enzymatic in operation.

[0033] In even further variations of the above noted aspects, and abovenoted variations, one or more of the following is provided: (1) a firstportion of the MD telemetry system is incorporated into the MD processorand a second portion of the MD telemetry system is external to the MDprocessor, (2) a first portion of the CD telemetry system isincorporated into the CD processor and a second portion of the CDtelemetry system is external to the CD processor, (3) the MD processorincludes an MD central processing unit and at least one other MDfunctional module, (4) the CD processor includes a CD central processingunit and at least one other CD functional module, (5) the MD electroniccontrol circuitry includes at least one external MD functional module,other than a portion of the MD telemetry system, that is external to theMD processor, or (6) the CD electronic control circuitry includes atleast one external CD functional module, other than a portion of the CDtelemetry system, that is external to the CD processor.

[0034] Still additional aspects of the invention set forth methodcounterparts to the above system aspects as well as to other functionalassociations and relationships, and processes that have not beenspecifically set forth above but will be understood by those of skill inthe art from a review of the teachings provided herein.

[0035] Further aspects of the invention will be understood by those ofskill in the art upon reviewing the teachings herein. These otheraspects of the invention may provide various combinations of the aspectspresented above as well as provide other configurations, structures,functional relationships, and processes that have not been specificallyset forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above referred to objects and aspects of the presentinvention will be further understood from a review of the description tofollow, the accompanying drawings, and the claims set forth hereafter,wherein:

[0037]FIG. 1a depicts a perspective view of the main body of theimplantable device of the first preferred embodiment;

[0038]FIG. 1b depicts a perspective view of the support and catheterassembly that attaches to the main body of the implantable device of thefirst preferred embodiment;

[0039]FIG. 2 depicts a perspective view of the external communicationdevice of the first preferred embodiment; and

[0040]FIG. 3 depicts a block diagram of the main components/modules ofboth the implantable device and the external communication device of thefirst preferred embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] Various details about the structural and functional configurationand operation of preferred ambulatory medical devices and preferredcommunication devices are found in several U.S. patent applicationsfiled concurrently herewith and incorporated herein by reference intheir entireties: (1) Docket No. USP-1075-A, (2) Docket No. USP-1075-A,(3) Docket No. USP-1077-A, (4) Docket No. USP 1078-A, and (5) Docket No.USP-1079-A.

[0042] U.S. patent application Ser. No. To Be Determined, filed on Jan.22, 2001 (concurrently herewith), by Starkweather, et al., entitled“Ambulatory Medical Apparatus and Method Having Telemetry ModifiableControl Software”, corresponding to Medical Research Group, Inc. DocketNo. USP-1075-A, is hereby incorporated herein by this reference as ifset forth in full herein. This application provides teachings concerningan implantable medical device (e.g. infusion pump) and handheldcommunication device wherein the implantable device is capable ofoperating under control of different software programs, wherein a firstprogram operates after resetting the implantable device and is notcapable of allowing significant medical functionality but is capable ofselected telemetry operations including telemetry operations that allowreplacement software to be downloaded, and wherein a second program maybe caused to take control of the device and enables medicalfunctionality and selected telemetry operations but is incapable ofreceiving replacement software. It is also taught that a software imagemay be received in multiple messages where each message is provided withits own validation code and wherein a validation code for the wholeimage is provided and wherein each provided validation code mustcompared to a derived validation code prior to accepting the validity ofthe replacement software.

[0043] U.S. patent application Ser. No. To Be Determined, filed on Jan.22, 2001 (concurrently herewith), by Bowman, et al., entitled“Ambulatory Medical Apparatus and Method using a Telemetry System withPredefined Reception Listening Periods”, corresponding to MedicalResearch Group, Inc. Docket No. USP-1077-A, is hereby incorporatedherein by the reference as if set forth in full herein. This applicationprovides teachings concerning an implantable medical device (e.g.infusion pump) and an external device that communicate with one anothervia telemetry messages that are receivable only during listeningwindows. Each listening window is open for a prescribed listening periodand is spaced from other listening windows by an interval. The listeningperiod is typically kept small to minimize power consumption. Toincrease likelihood of successful communication, the window may beforced to an open state, by use of an attention signal, in anticipationof an incoming message. To further minimize power consumption, it isdesirable to minimize use of extended attention signals, and this isaccomplished by the transmitter maintaining an estimate of prescribedlistening start times and attempting to send messages only duringlistening periods. In the communication device, the estimate is updatedas a result of information obtained with the reception of each messagefrom the medical device.

[0044] U.S. patent application Ser. No. To Be Determined, filed on Jan.22, 2001 (concurrently herewith), by Lebel, et al., entitled “AmbulatoryMedical Apparatus with Hand Held Communication Device”, corresponding toMedical Research Group, Inc. Docket No. USP-1078-A, is herebyincorporated herein by this reference as if set forth in full herein.This application provides teachings concerning an implantable medicaldevice (e.g. infusion pump) and handheld communication device (CD) thatexchange messages via telemetry such that commands are supplied to theimplantable device and operational information is obtained therefrom.The CD is controlled, at least in part, by a processor IC according to asoftware program operating therein and provides feedback to a user via avisual display, an audio alarm, and a vibrational alarm, and allowsinput from the user via a touch sensitive keypad. Certain inputfunctions are restricted by password. The visual display includes anicon and fixed element display region and a bitmap display region. Thefixed element display region includes time and date displays, batteryand drug level displays that decrement, and a moving delivery statedisplay. Various screens allow operational or log information to bedisplayed and/or user entry of commands. Program features when disableare removed from a series of screen options that can be scrolledthrough.

[0045] U.S. patent application Ser. No. To Be Determined, filed onJanuary 22, 2001 (concurrently herewith), by Starkweather, et al.,entitled “Method and Apparatus for Communicating Between an AmbulatoryMedical Device and Control Device Via Telemetry Using Randomized Data”,corresponding to Medical Research Group, Inc. Docket No. USP-1079-A, ishereby incorporated herein by this reference as if set forth in fullherein. This application provides teachings concerning an implantablemedical device (e.g. infusion pump) and handheld communication devicethat communicate with one another via telemetry wherein transmittedmessages have enhanced numbers of and/or regularity of bit transitionsto minimize the risk of synchronization loss between transmitted bits ofdata and received bits of data. It is taught that bit transitions forportions of messages may be enhanced by applying a pseudo-randomizationscheme to those portions of messages that are transmitted in a way thatallows the receiver to extract the original data from the receivedrandomized data. Preferred randomization techniques modify (i.e.randomize) the data using a CRC value that is being accumulated whilesimultaneously causing the modified data to modify subsequentaccumulation of the CRC itself. Upon reception, the reversal of datarandomization is then made to occur so that the intended message isappropriately received.

[0046] U.S. patent application Ser. No. To Be Determined, filed on Jan.22, 2001 (concurrently herewith), by Lebel, et al., entitled“Microprocessor Controlled Ambulatory Medical Apparatus with Hand HeldCommunication Device”, corresponding to Medical Research Group, Inc.Docket No. USP-1080-A, is hereby incorporated herein by this referenceas if set forth in full herein. This application provides teachingsconcerning an implantable medical device (e.g. infusion pump) andhandheld communication device. wherein an implantable infusion pumppossesses operational functionality that is, at least in part,controlled by software operating in two processor ICs which areconfigured to perform some different and some duplicate functions. Thepump exchanges messages with the external communication device viatelemetry. Each processor controls a different part of the drug infusionmechanism such that both processors must agree on the appropriateness ofdrug delivery for infusion to occur. Delivery accumulators areincremented and decremented with delivery requests and with deliveriesmade. When accumulated amounts reach or exceed, quantized deliverableamounts, infusion is made to occur. The accumulators are capable ofbeing incremented by two or more independent types of delivery requests.Operational modes of the infusion device are changed automatically inview of various system errors that are trapped, various system alarmconditions that are detected, and when excess periods of time lapsebetween pump and external device interactions.

[0047] The first embodiment of the present invention provides a longterm implantable medical delivery system that controllably suppliesinsulin to the body of a patient afflicted with diabetes mellitus. Thisembodiment includes an implantable medical device and an externalcommunication device. In the most preferred embodiments, thecommunication device is a hand held device that is used directly by thepatient to interact with the medical device as opposed to being limitedto use by a physician, nurse, or technician. It is preferred that thecommunication device provide (1) the ability to send commands to themedical device, (2) receive information from the medical device, and (3)be able to present to the patient at least a portion of the informationit receives from the medical device. In preferred embodiments, thepatient interacts with the medical device via the communication deviceat least once per week, on average, more preferably at least once everyother day, on average, and most preferably at least once per day, onaverage.

[0048] The implantable medical device (MD) includes a biocompatiblehousing; a reservoir within the housing for holding a quantity ofinsulin; a side port that attaches to the side of the housing, acatheter, that connects to the side port; a pumping mechanism, withinthe housing for moving the insulin from the reservoir through thesideport and through the catheter to the body of the patient; andcontrol, monitoring, and communication electronics located within thehousing. In alternative embodiments various portions of implantablemedical device hardware may be located outside the housing. For example,the pumping mechanism or a telemetry antenna may be located within thesideport or other side mounted housing; or a telemetry antenna maymounted on the outside surface of the housing, or extend along thecatheter

[0049] The external communication device (CD) communicates commands tothe medical device, receives information from the medical device, andcommunicates system status and system history to the patient. Theexternal communication device includes a housing; a keypad mounted onthe housing; a display forming part of the housing; and control,monitoring, and communication electronics located within the housing. Inalternative embodiments, the keypad may be replaced in whole or in partby a touch sensitive display or a voice recognition system. In addition,or alternatively, the display may be replaced in whole or in part by aspeech generation system or other audio communication system.

[0050] The outer appearance of the implantable device 2 is depicted intwo pieces in FIG. 1a and 1 b and includes housing 6 having a drugoutlet port 8, and a refill port 12, a removable sideport 14 that mountsagainst the side of the housing 6 over outlet port 8, and a catheter 16having a distal end 18 and a proximal end that attaches to sideport 14.In alternative embodiments, the implantable device may take on adifferent shape and/or the sideport may be removed in favor of apermanently mounted catheter assembly.

[0051] The outer appearance of the external communication device 32 isdepicted in FIG. 2. The various components of the external communicationdevice are fitted in or on housing 34. Housing 34 is divided into afront portion 34 a and a back portion 34 b. The front portion 34 a isprovided with an opening in which an LCD panel 36 is positioned. Thepanel 36 has a lower portion that is a bit map display and an upperportion that provides icons and fixed element displays. The frontportion 34 a of the external communication device is also provided witha five-element keypad 38. A first key 38 a is not located under a raisedpad and does not provide tactile feedback when it is touched and may beused for special functions. The remaining four keys 38 b, 38 c, 38 d,and 38 e have raised pads that provide tactile feedback when they aredepressed. These remaining keys may be used in normal device operationand are known as the select key, the up arrow key, down arrow key, andthe activate key, respectively. The back portion 34 b of the housing isfitted with a door under which a compartment is located for holding areplaceable battery.

[0052]FIG. 3 depicts a simplified block diagram of various functionalcomponents or modules (i.e. single components or groups of components)included in the implantable medical device 2 and external communicationdevice 32. The external communication device 32 includes (1) a housingor cover 34 preferably formed from a durable plastic material, (2)processing electronics 42 including a CPU and memory elements forstoring control programs and operation data, (3) an LCD display 36 forproviding operation for information to the user, (4) a keypad 38 fortaking input from the user, (5) an audio alarm 44 for providinginformation to the user, (6) a vibrator 46 for providing information tothe user, (7) a main battery 52 for supplying power to the device, (8) abackup battery 54 to provide memory maintenance for the device, (9) aradio frequency (RF) telemetry system 56 for sending signals to theimplantable medical device and for receiving signals from theimplantable medical device, and (10) an infrared (IR) input/outputsystem 58 for communicating with a second external device.

[0053] The second external device may include input, display andprogramming capabilities. The second device may include a personalcomputer operating specialized software. The computer may be used tomanipulate the data retrieved from the communication device or themedical device or it may be used to program new parameters into thecommunication device or directly into the medical device, or even usedto download new software to the communication device or to the medicaldevice. The manipulation of the data may be used in generating graphicaldisplays of the data to help aid in the interpretation of the data. Suchdata interpretation might be particularly useful if the medical deviceprovides data concerning a physiological parameter of the body of thepatient, such as a glucose level versus time. More particularly thecomputing power and display attributes of the second device might beeven more useful when the medical device includes both an implantedsensor (e.g. glucose sensor), or external sensor, and an implanted pump(e.g. insulin pump), or external pump, where the second external devicemay be used to enhance the ability to ascertain the effectiveness of thetwo devices working together. Successful control periods and problemcontrol periods could be more readily identified. In fact, if the twodevices work on a closed loop basis or semi-closed loop basis, theanalysis performable by the second external device may be useful inderiving new closed loop control parameters and/or in programming thoseparameters directly into the communication device or the medical deviceor devices.

[0054] The implantable device 2 includes (1) a housing or cover 6preferably made of titanium that may or may not be coated to enhancebiocompatibility, (2) processing electronics 72 including two CPUs andmemory elements for storing control programs and operation data, (3)battery 74 for providing power to the system, (4) RF telemetry system 76for sending communication signals (i.e. messages) to the external deviceand for receiving communication signals (i.e. messages) from theexternal device, (5) alarm or buzzer 82 for providing feedback to theuser, (6) refill port 12 for accepting a new supply of drug as needed,(7) reservoir 84 for storing a drug for future infusion, (8) pumpingmechanism 86 for forcing selected quantities of drug from the reservoirthrough the catheter to the body of the patient, (9) sideport 14 forproviding a replaceable connection between the (10) catheter and thepump housing and for allowing diagnostic testing of the fluid handlingsystem to occur, and catheter 16 for carrying medication from theimplant location to the desired infusion location.

[0055] In this embodiment, the pump mechanism is preferably a low power,electromagnetically driven piston pump. Such as for example Model Nos.P650005 or P650009 as sold by Wilson Greatbatch Ltd. of Clarence, N.Y.which have stroke volumes of 0.5 microliters and draw under 7 mJ (e.g.about 6 mJ) per pump stroke and under 4 mJ (e.g. about 3 mJ) per pumpstroke, respectively. The pump mechanism dispenses a sufficiently smallvolume of insulin per stroke so that a desired level of infusionresolution is achieved. For example if an infusion resolution of 0.2units of insulin were desired when using U400 insulin, then a strokevolume of about 0.5 microliters would be appropriate. In otherembodiments other types of infusion pumps may be used, e.g. peristalticpumps.

[0056] As depicted in FIG. 3, the implantable device includes areservoir 84 for holding a desired quantity of insulin. In thisembodiment, the drug held in the reservoir is preferably maintained at aslight negative differential pressure (with respect to the pressure onthe outside of the housing) so that in the event of a leakage in thereservoir 84 or housing 6, the drug will not be forced from the housinginto the body of the patient. The drug is added to the reservoir 84 bymeans of a transcutaneous needle that is passed from a position exteriorto the body into self sealing refill port 12. Due to the slight negativepressure that the reservoir experiences, insulin in a syringe connectedto the needled is drawn into the reservoir without need of externalforce. The drug is extracted from the reservoir 84 and forced throughcatheter 16 by an electronically controlled pump mechanism 86. Inalternative embodiment positive pressure reservoirs may be used incombination with pumping mechanisms that force the medication or drugfrom the implantable device and/or used with flow restrictors thatdispensed the drug at a fixed rate or at a variable rate with the aid ofvalves or flow diverters.

[0057] The size of the reservoir is preferably large enough to holdsufficient insulin so that refilling does not have to occur too often.For example, it is preferred that time between refills be within therange of 1.5-4 months or longer, more preferably at least 2 months, andmost preferably at least 3 months. Opposing the containment of a largevolume of insulin, is the desire to keep the implantable device as smallas possible. In the present embodiment the implantable device andreservoir has been designed to hold about 13 ml of insulin. A preferredinsulin has a concentration of 400 units per milliliter and is availablefrom Aventis HOE 21Ph U-400 from Aventis Pharma (formerly Hoechst MarionRoussel AG, of Frankfurt am Main, Germany). This insulin is a highlypurified, semi-synthetic human insulin with 0.2% phenol as a preservingagent, glycerol as an isotonic component, TRIS as a buffer, plus zincand Genopal® as stabilizing agents. This quantity and insulinconcentration allows about 2-4 months between refills. In otherembodiments higher insulin concentrations may be used (e.g. U-500 orU-1000) to increase time between refills or to allow reduction inreservoir size. In some embodiments, when higher concentrations areused, any quantized minimum delivery amounts may be reduced by modifyingthe pumping mechanism, control circuitry, or software control algorithmso that infusion resolution is not adversely impacted.

[0058] The external communication device contains appropriate softwareto provide proper control of the device including appropriatefunctionality to allow communication with the medical device, to allowadequate control of the operation of the medical device, and to giveappropriate feedback to the user regarding overall system operation. Themedical device is provided with appropriate software to allowcommunication with the external communication device, to allow safe andappropriate operation of the medical functionality of the device, and toallow direct feedback to the user concerning device status via theinternal alarm.

[0059] The control electronics of both the implantable device andexternal communication device are centered around microprocessor basedintegrated circuits, i.e. processor ICs, that are implemented in thepresent embodiment in the form of application specific integratedcircuits (ASICs). In the present embodiment, the control electronics ofthe implantable device are centered around two identical ASICs that aremounted on a hybrid circuit board. In some alternative embodiments asingle ASIC may be used, or a single dual processor integrated ASIC maybe used. In a single processor device one or more circuits may beprovided to monitor the operation of a CPU in the processor to ensure itcontinues to operate properly in one or more key functions. In thesingle dual processor integrated ASIC, dual circuitry would be providedso that each processor could act independently of the other. In thesingle dual processor embodiment, a single off-circuit oscillator may beused to drive both processors or each may have an independentoscillator. A single chain of timing circuits could be used in drivingboth processors or independent chains of timing circuits could be used.Furthermore, if a single oscillator is used to drive both processors,then one or more separate circuits such as a counter and an RC timer maybe used to verify appropriate operation of the oscillator and/or anyparticular timing circuit dependent thereon.

[0060] In different embodiments, more or less of the control electronicsmay be implemented within one or more processor ICs while any remainingportions may be implemented external to the processor ICs. The processorIC may be referred to as an MD processor if used in the medical deviceportion of the system or a CD processor if used in the communicationdevice portion of the system. In other embodiments the process IC usedin the communication device may be different, e.g. have a different CPUor different peripheral modules, from a processor IC used in the medicaldevice. In embodiments where more than one processor IC is used ineither the medical device or the communication device each of theprocessors may be different. They may be specifically designed for theirintended roles when they perform at least partially different functions.Depending on particular design constraints portions of the electronicsnot embodied in the processor ICs may form part of one or more hybridcircuit boards or be otherwise mounted within, on, or even in some casesexternal to a device housing.

[0061] Each processor IC of the present embodiment includes a 16-bitcore CPU which is a CMOS low power version of the INTEL 8086 processorand various peripheral modules that are used for system control, dataacquisition, and interfacing with electrical components external to theprocessor IC.

[0062] The peripheral modules of the processor IC include (1) anon-volatile memory interface module, e.g. a SEEPROM interface module,(2) a boot ROM module; (3) an SRAM module; (4) a memory decoder module;(5) a crystal oscillator module; (6) a timer module; (7) a pumpinterface module; (8) a watchdog module; (9) an RF module; (10) aninterrupt handler module; (12) an analog-to-digital converter module;(13) an LCD clock driver module; (14) an alarm interface module; and(15) first and second synchronous serial interface modules.

[0063] In alternative embodiments fewer, additional, or differentperipheral modules may be incorporated into the processor ICs. In oneextreme the processor IC may simply incorporate a CPU with all othermodules being external thereto. In the other extreme almost all, if notall, electronic components may be incorporated into a single processorIC. Intermediate alternatives might incorporate a single additionalmodule into the processor IC (in addition to the CPU), others mightincorporate more than one, e.g. 4 or more, 8 or more, or the like. Instill other alternatives, the number of peripheral modules or componentsin an entire device may be considered and more than a certain percentageof them incorporated into one or more processor ICs, e.g. more than 50%,more than 75%, or even more than 90%.

[0064] The processor ICs are responsible for basic system management andcommunication of information between the implantable device and theexternal communication device through the RF telemetry link. Thetelemetry systems of the present embodiment are implemented in partthrough electrical hardware and in part through software controlled by aprocessor IC.

[0065] In the present embodiment, most of the required electricalmodules for the implantable device are integrated within the processorICs. However, several are not. These additional modules include twoindependent crystal oscillators (one for each ASIC); two non-volatilememory modules (one for each ASIC), e.g. SEEPROM chips; a volatilememory module (used only by one of the ASICs), e.g. an SRAM chip; pumpdriver circuitry (partially controlled by the each ASIC); front endtelemetry system circuitry; and voltage measurement circuitry associatedwith the pump driver circuit; a buzzer; and a battery.

[0066] Within the implantable device telemetry operations are controlledby a single ASIC (sometimes known as the main processor) The otherprocessor (sometimes known as the monitor processor) controls the buzzerand is thus responsible for audio communications coming from theimplantable device. The medical functionality of the implantable device(i.e. the administration of insulin in the present embodiment) iscontrolled by both processors. To maintain the implantable device in afail safe operational mode, these two processors maintain an appropriatelevel of agreement concerning infusion instructions an error conditionresults and either pumping is halted or a system reset may be made tooccur. The main and monitor processors communicate with each otherthrough the use of hardwired serial input and output ports.

[0067] As with the implantable device, the control electronics of theexternal communication device are centered around an ASIC that controlsand interacts with a number of peripheral modules. These peripheralmodules include an LCD display and driver, an IR port and driver, acrystal oscillator, a keypad and keypad interface, power managementmodules and reset circuitry, external volatile memory (e.g. SRAM) andnon-volatile memory (e.g. SEEPROM), a buzzer, and front end telemetryhardware.

[0068] The telemetry system for the implantable device and the externalcommunication device provide a half-duplex link between each other usinga carrier frequency of about 250 kHz (e.g. about 2¹⁸ Hz) and a datasignal having a frequency of about 8 kHz (e.g. about 2¹³). Thetransmitter hardware uses the 8 kHz data signal to modulate the carriersignal to generate signals that will be transmitted by the antenna. Thereceiver hardware receives the modulated signal and demodulates it toextract the 8 kHz data signal. Both the implantable device and theexternal communication device have transmit and receive capabilities toallow two-way communication.

[0069] Most of the RF telemetry circuits necessary for communicationbetween the external communication device and the implantable device areimplemented in the processor IC. In order to minimize the digital noiseinterference that the processor IC might impart to the weak RF signalsthat are being received, a high-gain RF amplifier is implementedoff-chip. Also an RF antenna, that is used for both transmission andreception, and circuitry to select between reception and transmissionare implemented off-chip. The remaining analog sections and all thedigital demodulation circuits are implemented in the processor IC.

[0070] The RF module of the processor IC outputs in phase and quadraturephase signal components for combined transmission by the externalantenna. The RF module also supplies a control signal that is used toswitch between a transmission configuration and a receptionconfiguration. The RF module receives as inputs signals from theamplification circuitry.

[0071] A Quadrature Fast Acquisition Spread Spectrum Technique (QFAST®)is used as the modulation technique. QFAST® modulation is based on anOffset Quadrature Phase Shift Keying (QPSK) modulation technique. Inthis technique, data generated by the CPU modulates clock signals at thecarrier frequency. As a result of quadrature modulation, in-phase andquadrature-phase components of the given data stream are generated. Thetwo components are then applied to opposite ends of the external antennaso that a combined signal is transmitted.

[0072] As noted above, external to the processor IC, the received RFsignal is amplified by a high gain receive amplifier. A bandpass filteris used to attenuate out-of-band components such as those due to AMradio stations. The amplified RF signal then enters a mixer in the RFmodule of the processor IC and is converted to baseband using twomixers, one in-phase mixer and one quadrature phase mixer both at thecarrier frequency. The mixer outputs are the quadrature components ofthe baseband signals. An integrator & dump function in the RF modulethen removes the sum frequency (2 fc) and high frequency noise (i.e.acting as a low pass filter) from each of the two signals. The processedsignals are then digitized using a comparator and passed to thedemodulator where the data and clock are recovered.

[0073] In QFAST®, data rate adaptability is accomplished through aspread-spectrum “coding gain” concept, with the spreading code being asimple clock. The modulation produced by the QFAST® modulator isdemodulated in a manner which delivers both clock and data. All of theQFAST® modulation and demodulation circuits are digital and areincorporated into the processor IC.

[0074] The QFAST® technique provides a communication system with anumber of attributes: (1) it extracts the clock from the received signalwithout a clock recovery loop; (2) it provides demodulation of datawithout phase ambiguity and without the requirement for synchronousdemodulation; (3) it makes effective use of the available transmissionbandwidth, (4) it results in fast acquisition of the message signal; (5)it is relatively immune to the effects of highly dispersive anddistorting propagation media; (6) it does not require regeneration of aphase-coherent local replica at the receiver of the transmitted carrier;(7) it does not require resolution of ambiguity between the in-phase andquadrature-phase channels in the receiver; and (8) it does not exhibitdata phase ambiguity.

[0075] Further detail about QFAST® (Quadrature Fast Acquisition SpreadSpectrum Technique) may be found in U.S. Pat. No. 5,559,828, entitledTransmitted Reference Spread Spectrum Communication Using a SingleCarrier with Two Mutually Orthogonal Modulated Basis Vectors, byArmstrong, et al.

[0076] The RF module in the processor IC consists of timing circuitry,circuitry to maintain time synchronization between the implantabledevice and the external communication device, a digital RF transmittersection that includes a QFAST® RF modulation transmitter, an analogreceive module, and a digital receive section that includes a QFAST® RFmodulation receiver.

[0077] Further details about the structural and functional configurationand operation of preferred ambulatory medical devices and preferredcommunication devices are found in several U.S. patent applications.

[0078] The RF communication between the implantable device and theexternal communication device occurs in the form of messages (sometimesreferred to as communication signals or packets) that are passed backand forth between the two devices. In this embodiment these messageshave a multi-part format or protocol: (1) preamble, (2) frame sync, (3)telemetry identifier, and (4) data.

[0079] In other embodiments other multipart formats may be used. Forexample, the multipart format might consist of (1) a preamble, (2) atelemetry identifier, and (3) data. In still other embodiments thepreamble and frame sync may be combined into a single entity or thetelemetry identifier and the frame synch may be combined into a singleentity, or even all of the preamble, frame sync, and telemetryidentifier may be combined into a single entity such that thefunctionality of associated with these individual elements of themessages of the present embodiment may be performed simultaneously or inseries based on a single but repeated pattern of information.

[0080] For communications from the implantable device to the externalcommunication device the preamble is a repeating pattern of “10”, i.e.10101010. This alternating pattern of ones and zeros is broadcast for8-bit times. This pattern is considered the standard preamble pattern.In other embodiments this standard preamble pattern may be differentfrom that noted above (e.g. it may be a repeated pattern of “01” insteadof “10”). Though, unnecessary, the standard preamble need not transitionwith every other bit though, as a certain number of bit transitions aretypically necessary to establish bit synchronization, the moretransitions, the shorter the minimum length that the preamble can take.

[0081] For communications from the external communication device to theimplantable device, the preamble is either of the standard preamblepattern but applied for an extended number of bit times (e.g. 24, 48, or96) or is of an attention preamble pattern that is applied for,typically, even a longer extended number of bit times. In otherembodiments, not only may the preamble used by the implantable deviceand the external communication device have different lengths as used inthis embodiment, they may also use different standard preamble bitpatterns. Of course in still other embodiments, a same preamble lengthmay be used by both the implantable device and the externalcommunication device whether or not the same standard preamble bitpattern is used. The attention preamble pattern is formed of a repeatedpattern of “110110 . . . 110”.In other embodiments, other attentionpreamble patterns may be used (e.g. repetitions of “011”, “100”, “001,“1011”, and the like).

[0082] The preamble, whether of the standard pattern or the attentionpattern, is used so that the RF reception hardware can establish bitsynchronization (i.e. bit boundary recognition) of the incoming data.However, the attention preamble is further used to get and hold thereceiver's attention for a defined period of time. As long as theattention preamble is being received, the receiver's hardware will stayon and continue tracking the signal in anticipation of an incomingmessage. In other embodiments, the concept of a standard preamblepattern that will not hold the receiver's attention may be dispensedwith in favor of always using a preamble that is in effect an attentionpreamble.

[0083] The attention preamble is considered to be lost, or no longerbeing received, when the receiver receives more than 2 inappropriate bitvalues during receipt of any 64-bits or when the frame sync pattern isreceived.

[0084] Before beginning error detection, the receiver's hardware firstrequires that the receipt of the attention preamble be established. Inestablishing receipt of the attention preamble the receiver's hardwaremay load the received bits into a shift register and may then comparethe shifting pattern to a predefined pattern of selected length and thenmay consider the receipt of the attention preamble to be establishedonce the comparison indicates a match of sufficient length has occurred,The receive hardware then continues to compare received bits topredicted bits based on the pattern established. A bit counter isincremented with each bit received and an error counter is incrementedwith each error detected. The bit counter is reset whenever an error isdetected. The error counter is reset whenever the bit counter reach apreset value. If the error counter should reach a predefined erroramount, the established attention preamble is considered to have beenlost and if the receiver is still operating within its listening period,the receiver's hardware continues its process of trying to establishreceipt of attention preamble. The parameters associated withestablishing receipt of the attention preamble and associated with thesetting of error tolerances may be hardcoded into the system or they maybe programmable into hardware registers.

[0085] It is preferred that the above analysis be implemented inhardware due to the energy savings possible but in other embodiments theprocess may be implemented via software.

[0086] Of course in other embodiments, the error tolerance believedacceptable may be increased or decreased or defined in a differentmanner. For example, instead of using an error tolerance of 2-bits outof 64-bits, one might use a tolerance of {fraction (1/32)}.

[0087] The tolerance may even be increased to {fraction (2/32)},{fraction (3/64)}, {fraction (4/64)}, or even higher.

[0088] Alternatively, it may be decreased to {fraction (1/64)},{fraction (1/128)} or even to zero.

[0089] The attention preamble may be used when there is some uncertaintyin the time synchronization of the two devices. The extra length of theattention preamble allows the receiver's reception window to open alittle later than anticipated and to still have the receiver pick up theentire message. The extra length of the attention preamble allows thereceiver's reception window to open earlier than anticipated, so long asa minimum number of bits are heard by the receiver during the time itsreception window is normally open, and still have the receiver'sattention locked onto the preamble and have the receiver remain on aslong as the attention preamble is being received, plus a little more, inanticipation of receiving a frame sync pattern.

[0090] The receiver may miss some of the initial bits in the preamblebut a minimum number of bit transitions (e.g. 4, 6, or 8 transitions) ofthe preamble pattern must be received to ensure bit synchronizationbetween the transmitted message and the receiver. In the presentembodiment, the implantable device broadcasts with a minimal preamblesize in order to reduce power consumption within the implantable device.In other embodiments, the preamble used by the implantable device may belarger relative to the minimum number of bit transitions needed toestablish bit synchronization.

[0091] In the present embodiment, frame sync may actually be consideredbyte sync (i.e. frames are bytes) and is a single byte of a selectedpattern and is used so the receiver can obtain byte boundaries for thetransmitted data. In the present embodiment, the selected pattern is“10110000”.In other embodiments, other patterns, pattern lengths, andframe sizes may also be acceptable for use as frame sync so long as thepatterns (in combination with preamble or attention preamble patternsand any tolerances in their reception) cannot lead to errors in definingbyte transitions. In still other embodiments, the attention preamblepattern may be of the same bit pattern as the frame sync, in which case,some error tolerance may be allowed in the frame sync pattern and thereceiver's attention would be held until the pattern is lost or a validtelemetry ID pattern is received. This latter alternative requires thatvarious potential telemetry IDs be disallowed.

[0092] Even during the receipt of attention preamble (or other preamble)the receiver continually compares shifting bits that are received to theanticipated frame sync pattern. The Frame Sync byte may be detected byfeeding the incoming bit stream into a shift register and passing thebit values in the register to the inputs of an 8 input AND gate whoseinput assertion levels correspond to the anticipated frame sync pattern.

[0093] This comparison process continues so long as the receivercontinues to listen for an incoming message or until a valid frame syncpattern has been received. If the receiver is continuing to listenbeyond its normal reception window (i.e. listening period), due to thereception of an attention preamble, the listening will not stopimmediately upon the attention preamble being lost. The comparisonprocess for ascertaining the receipt of frame sync continues for anumber of bits after attention preamble is lost, even if the listeningperiod has ended, as its loss may be associated with the partial receiptof frame sync. Once frame sync is received a valid frame sync signal isasserted.

[0094] In the present embodiment, the telemetry identifier (i.e.telemetry ID) is a 3-byte value that is used to ensure that only theintended receiver receives a message. The value of all “1s” indicates auniversal message that is to be received by all receivers, otherwise thetelemetry ID must be agreed upon between the receiver and transmitter. Aunique ID is provided for each implantable device and each externalcommunication device during manufacturing. Only the externalcommunication device can transmit a message using the universal ID code.The telemetry IDs that the receiver will consider to be valid are the IDof the receiver or the universal ID. All other incoming bit patternswill be rejected with the result that the receiver will be either turnedoff or will start again looking for a valid frame sync pattern attentionpreamble. In alternative embodiments, instead of the receiver acceptingonly its own ID (in addition to the universal ID) it may instead acceptthe ID of the transmitter. In other alternative embodiments, a differentlength preamble may be used by the implantable device and the externalcommunication device. In still further alternatives, the telemetry IDsmay not be unique if it is believed that the chance of miscommunicationbetween devices is not a significant risk. In fact, if there is littlerisk of miscommunication, telemetry ID may be dropped from the messageprotocol.

[0095] Other embodiments may retain the concept of telemetry ID foreither the receiver or the transmitter or both but only pass thetelemetry ID information implicitly. Such implicit transfer might usethe telemetry ID information in generating a validation code (e.g. CRC)that is transferred with the message. In such cases the receiver couldcompare the received code to one or more different codes generated usingeach of the unique telemetry ID and the universal telemetry ID. Theseembodiments would be less preferred when power consumptionconsiderations are critical, as the telemetry system of the receiverwould have to remain on to receive the entire message in order todetermine whether the message was for it or not.

[0096] After a Frame Sync byte is detected, the processor IC hardwarecompares the next 24 bits of the incoming data to the personal ID bitsand to the universal ID which in this embodiment is fixed at 0×FFFFFF.If a valid telemetry ID is received, the receiver listens to theremaining portion of the message. If a valid telemetry ID is notreceived listening by the receiver may be aborted, if the listeningperiod has expired, or listening for attention preamble and frame syncmay continue, if the listening period has not yet expired.

[0097] In alternative embodiments the frame sync and telemetry ID may becombined into a single entity that is identified as a whole as opposedto the present embodiment where the two pieces are looked for andidentified separately.

[0098] In the present embodiment, data is provided in an integer numberof bytes following the telemetry ID. In the present embodiment the firstbyte of the data indicates the message type. The first seven bits of thefirst byte is an operation code or op-code while the eighth bit iseither ignored or is set and interpreted as a sequence number (to bediscussed hereafter) dependent on whether or not the first seven bitscall for a sequence number or not. Each op-code, based on its nature, isfollowed by data in a defined number of bytes. The specific op-codeitself may dictate the number of bytes that follow or alternatively thespecific op-code may dictate that the number of bytes to follow may beextracted from the first byte or several bytes of information thatfollow it. In alternative embodiments, op-codes may have a differentlength, or not be used at all, the message length or message end may bedictated in other ways. Based on the op-code and potentially one or morebytes following it, the receiver knows exactly how many more bytes ofdata to listen for. After receiving those bytes, the receiver may beturned off to conserve power.

[0099] For some messages dealing with drug delivery, the data portion ofthe message may include a bolus number. The bolus number is similar tothe sequence number in that it is incremented by both the implantabledevice and external communication device under controlled conditions soas to reduce the possibility of bolus requests being delivered more thanonce when duplicate requests may be made as a result of the externalcommunication device failing to receive a confirmation that a previousrequest was received. The bolus number may be a single bit number insome embodiments but in more preferred embodiments it is a multibitnumber (e.g. 2-bit, 4-bit, 7-bit, 1-byte, or 2-bytes) so that it cantake on more than two values thereby making it less likely that an errorwill escape detection due to received and expected numbers erroneouslymatching. The incrementing of the bolus number may occur within theexternal communication device when it receives confirmation that amessage was correctly received and it may be incremented by theimplantable device when it correctly receives a bolus request. As suchwhen a duplicate request for a bolus is received by the implantabledevice it can recognize that the expected and received bolus numbers donot match and that requested bolus is not a new request. As such theimplantable device can respond to the repeated request that the boluswas correctly received and delivered (with out performing a seconddelivery and without incrementing its expectation of what the next bolusnumber will be).

[0100] In other embodiments, other incrementing numbers may be used tohelp ensure that only appropriate operation of the implantable deviceoccurs. For example, incrementing temporary basal rate numbers may beused, and/or separate incrementing numbers may be used for differenttypes of boluses that might be requested, e.g. phase 1 boluses and/orphase 2 boluses. In still further alternatives, incrementing messagenumbers may be generally used. These message numbers may for example beused on all messages that have responses associated therewith. Once thereceiver confirms that a message was appropriately received it mayincrement its message number. Similarly, once the transmitter gets aresponse to the message it sent, it may likewise increment its messagenumber.

[0101] In the present embodiment, the data portion of the message endswith a one or 2-byte validation or error checking code (its type isdictated by the op-code included with the message). The preferred errorchecking code of this embodiment is in the form of a cyclic redundancycode (CRC). In other embodiments, the CRC may be replaced with anothererror checking code and/or it may be placed in a different part of themessage or even deleted from the message protocol completely. Theop-code may also be placed in another part of the message, or deleted infavor of other techniques that may be used in interpreting the messageand for determining when the end of the message has been properlyreceived.

[0102] In the present embodiment it is preferred that the CRC occur atthe end of the message as it simplifies the computational efficiency ofconfirming the validity of the message by the receiver. In alternativeembodiments, where message compilation and transmission occur inparallel, placing the CRC at the end of the message also allows the datato be processed and transmitted in a single pass without a need to havestorage space for the entire message available.

[0103] In the present embodiment, the telemetry system may lose bitsynchronization if insufficient bit transitions are received per unittime (e.g. if more than about 100 to 120-bit times lapse withoutreceiving a transition. In order to ensure that a sufficient number ofbit transitions occur, the data portion of the message, with theexception of the op-code is randomized prior to transmission and isde-randomized upon receipt. In alternative embodiments, at the cost ofsending more data, instead of randomizing the data, periodic bytes ofdata with transitions may be added to the protocol (e.g. after everyfifth or tenth byte of data ,a byte, or at least two bits, may betransmitted for the purpose of ensuring that a transition occurs so thatbit synchronization is maintained). In further alternatives, as shortmessages may not be subjected to improper reception due to loss of bitsynchronization, randomization may be limited to use with longermessages (e.g. messages with data portions longer than 10 to 15-bytes).

[0104] In order to keep power requirements low in a preferredimplementation, the external communication device and implantable deviceattempt to maintain a common time base, transmissions are set to startat specified times, and reception windows are set for specified timesand lengths. In this way, the receiver may remain in a powered down modemost of the time and can turn on to listen for a potential incomingmessage at the specified times for the specified lengths of time. If amessage is found to be incoming, the receiver stays on, otherwise itgoes back to sleep (i.e. power down mode).

[0105] In the present application, to avoid ambiguities in some portionsof the lo description relating to the timing associated with thetransmission and reception of messages, the following definitions willbe used: (1) “inbound” will generally refer to activities associatedwith telemetry reception by the medical device, whether implanted ornot, or to activities associated with telemetry transmission by thecommunication device, (2) “outbound” will generally refer to activitiesassociated with the telemetry transmission by the medical device,whether implanted or not, or to activities associated with telemetryreception by the communication device.

[0106] According to a telemetry timer in the medical device, outboundtransmissions begin at an “outbound transmission start time” andcontinue for an “outbound transmission period” which defines the periodthat the preamble portion of the message is sent either in terms of timeor in terms of the number of data bits. Similarly, according to atelemetry timer in the communication device, inbound transmissions beginat an “inbound transmission start time” and continue for an “inboundtransmission period” which defines the period that the preamble portionof the message is sent either in terms of time or in terms of the numberof data bits.

[0107] Furthermore, according to the telemetry timer in the medicaldevice, the telemetry reception system of the medical device beginslistening for messages at an “inbound listening start time” andcontinues to listen for an “inbound listening period” which may bethought of in terms of a time period or a given number of data bits.Similarly, according to the to the telemetry timer in the communicationdevice, the telemetry reception system of the communication devicebegins listening for messages at an “outbound listening start time” andcontinues to listen for an “outbound listening period” which may bethought of in terms of a time period or a given number of data bits.Additionally an “inbound listening interval” may be defined as theinterval between the successive inbound listening start times while an“outbound listening interval” may be defined as the interval between thesuccessive outbound listening start times. Throughout the specification,the above timing elements may be referred to in different waysparticularly when it is believed that the intended meaning is clear fromthe context of the description. However, when the precise meaning isrequired, descriptions will be based on the above definitions so as toremove ambiguity.

[0108] In the present protocol, no more than one message can be receivedfor each reception window or listening period. In alternativeembodiments, however, a “multiple message op-code” and a “number ofmessages parameter”, or the like, may be used such that the receiverknows that it must remain on until an indicated number of messages havebeen received.

[0109] As noted above, in a preferred implementation of the presentembodiment, telemetry hardware is used to identify the bit sync, framesync, and telemetry ID portions of an incoming message as opposed tousing software to interpret the initial bytes of a potential incomingmessage. After the hardware confirms that the incoming message is forthe particular receiver, the hardware activates the CPU of the processorIC so that software can aid in receiving, interpreting, and validatingthe message. This allows the power consumption of the receiver to remainat a minimum level while waiting for incoming messages to be initiallyscreened. Also as noted above, in a preferred implementation thereceiver only listens for incoming messages at discreet intervals forlimited periods so as to further minimize power consumption associatedwith maintaining communication. As it is preferred that the limitedlistening periods are relatively small compared to the listeningintervals, it is preferred that a reasonable level of timesynchronization be maintained between the transmitter and receiver so asto minimize excess power consumption and user inconvenience associatedwith using extended attention preambles, multiple communicationattempts, or the like, to ensure appropriate information transfer isachieved.

[0110] In alternative embodiments, particularly where power consumptionis less critical, the power of the microprocessor might be utilized tocontrol the telemetry hardware during the reception of any or all of thepreamble, frame sync, or telemetry ID portions of the message or mayeven be used to activate the reception hardware at the listening starttime and to deactivate the hardware at the end of the listening periodif it is determined that no message was incoming.

[0111] In a preferred time synchronization implementation, the conceptof time at the second and subsecond level is dictated by the implantabledevice, whereas the concept of time at the minute and hour level isdictated by the external communication device. Of course, othersynchronization schemes may be alternatively defined.

[0112] In the present embodiment, transmissions are allowed to beginonly at the beginning of a second as measured by the transmitter'stelemetry timer. Selected seconds boundaries within each minute areassigned either as a potential outbound transmission start time from theimplantable device to the external communication device or as apotential inbound transmission start time from the externalcommunication device to the implantable device (e.g. each even secondmark may represent a potential start time for inbound transmissions,while one or more odd second marks during each minute representpotential start times for unsolicited outbound transmissions. Apredefined inbound transmission start time may be replaced bytransmission start time for a solicited outbound message as the externalcommunication device is awaiting a response to the communication thatsolicited the response from the implantable device. In otherembodiments, potential transmission times may be set to start onsomething other than boundaries of seconds. In still other embodiments,the external communication device may continue to transmit messagesbased on inbound transmission start times as the implantable device maybe listening only during predefined inbound listening periods, while theimplantable device may be able to transmit at any time, outside of itsnormal predefined listening time slots, as the external communicationdevice may be continuously listening for outbound communications anytime it is not transmitting, or setting its outbound listening intervalto a small value (e.g. a opening of its reception window for smallperiods every few milliseconds) to see if any messages are incoming.This may be acceptable as power consumption in the externalcommunication device is less critical than in the implantable device.

[0113] In the present embodiment, depending on the type of message, a1-byte or 2-byte cyclical redundancy code (CRC) follows the data bytes.It is preferred that the CRC be generally computed using the telemetryID of the message originator (i.e. the telemetry ID of the transmitter).This serves as a form of security. If a message with this type of CRC isreceived by an implantable device, the implantable device must haveadvanced knowledge of the telemetry ID of the transmitting externalcommunication device or the implantable device will reject the messagebecause of a CRC error. Similarly the communication device may simplyreject messages that do not originate from its partnered medical device.

[0114] A CRC to be included with a message, in the present embodiment,is calculated based on the successive bytes forming the message andpossibly upon the identity of the transmitter as well. When the CRC iscomputed using the telemetry ID of the message originator, the firstthree bytes used in the calculation are the telemetry ID of theoriginator. The CRC calculation then uses the three bytes of thetelemetry ID of the intended receiver, the 1-byte of op-code, and thenthe remaining bytes of data in the message (with the exception of theCRC itself that is being calculated). When the CRC is not computed withthe message originator's telemetry ID, the CRC is computed based on thebytes of the message starting with the message op-code, and continuingwith the rest of the bytes in the data (with the exception of the CRCitself that is being calculated). Of course, in other embodiments, theCRC calculations may use the telemetry ID of the originator other thanat the beginning of the calculation. In still other embodiments, theop-code may be left out of the CRC calculation. In still otherembodiments, the order in which the components of the messages arecalculated may be changed, though if different from the order presentedin the message itself, recalculation of the CRC by the receiver may notbe able to be performed on the fly as the message is being received asis done in the current embodiment.

[0115] In the present embodiment, it is preferred that a precalculatedCRC transmission key and a precalculated CRC reception key are derivedand stored so that they do not have to be calculated each time they areneeded. The transmission key is a CRC derived from the byte-by-byteprocessing of the transmitter's three byte telemetry ID followed by thereceiver's three byte telemetry ID. The reception transmission key is aCRC derived from the byte-by-byte processing of the transmitter's threebyte telemetry ID followed by the receiver's three byte telemetry ID.Though these key definitions sound the same it must be remembered thatthe transmitting and receiving roles and devices are reversed. Thesekeys are used as the starting points for deriving the CRC that is to betransmitted with the message and the CRC that is derived upon receipt ofa message, respectively. In other embodiments other keys may be defined.

[0116] Further details about CRC generation may be found in (1) abovereferenced concurrently filed U.S. patent application No. (Docket No.USP-1079-A), (2) the “CCITT Red Book”, Volume VIII, published byInternational Telecommunications Union, Geneva, 1986, RecommendationV.41, “Code-Independent Error Control System”, and (3) “C Programmer'sGuide to Serial Communications”, 2nd Edition, by Joe Campbell, publishedby SAMS Publishing, Indianapolis, Ind., ISBN 0-672-30286-1. Inparticular chapter 3 of this latter book deals with errors and errordetection including CRCs, while chapter 23 deals with calculation ofCRCs. These books are hereby incorporated by reference herein as if setforth in full.

[0117] In a preferred implementation, the clock in the implantabledevice is the master clock in terms of tracking seconds within a minuteand subseconds within a second. The implantable device obtains itsconcept of the minute number within an hour and hour within a day fromthe values set in the external communication device which typicallycorrespond to the time of day at the patient's location. The values forsubseconds within a second are preferably transmitted implicitly by theimplantable device to the external communication device based on theimplicit understanding that implantable device transmissions alwaysstart at second boundaries.

[0118] More specifically, each time the external communication devicereceives a transmission from the implantable device, it uses acombination of elements to calculate a difference between the externalcommunication device clock and the implantable device clock. Theseelements include (1) the exact time that a certain portion of thetransmission is received according to the external communication deviceclock, (2) knowledge that implantable device message transmission beginsa known time according to the implantable device's clock, and (3) aknown time difference between that portion of the transmission and thebeginning of the transmission. These three elements may be used todetermine any difference in time between the clocks and ultimately toresynchronize the clocks. Of course, in alternative embodimentssynchronization may be implemented in other various ways.

[0119] In a preferred implementation, telemetry transmission andreception time slots begin exactly at one-second boundaries. Some timeslots are unassigned while others are assigned as slots forcommunications that are inbound to the implantable device. During normaloperation each even second, relative to the minute mark, is slotted forinbound transmissions. In a storage mode, the 0, 15, 30, and 45 secondmarks are slotted for inbound communications. Storage mode is a state ofthe implantable device where power consumption is reduced to a minimumlevel during periods of non-use thereby conserving battery power andthus extending the life of the implantable device. The one second markafter the roll over of each minute is assigned as a slot for unsolicitedoutbound messages (i.e. messages that are sent without a triggeringmessage from the external communication device). Messages sent from theimplantable device in response to external communication devicecommunications (i.e. solicited messages) are sent out on the nextavailable second mark. In alternative embodiments, it is apparent thatother inbound and outbound slots may be defined.

[0120] Since most system communications of the present embodimentoriginate with the external communication device, and as a rapidresponse to programming commands is desired for user convenience, it ispreferred that inbound slots be placed relatively close together (e.g.no more than 15 seconds apart, more preferably no more than 10 secondsapart, and even more preferably no more than 5 seconds apart, and mostpreferably no more than about 2 seconds apart. In order to save batterypower on the implantable device, it is generally preferred that thesystem have relative few outbound slots so that the implantable devicedoesn't consume excessive power when unsolicited messages from theimplantable device are not often used. In general, it is preferred thatthere be more predefined inbound time slots per time period thanoutbound time slots. Of course in alternative embodiments outbound timeslots may exceed or equal the number of inbound time slots.

[0121] When the external communication device sends an inbound messagethat requires a response, the external communication device listens forthe anticipated response from the implantable device that will be sentout on the next one second boundary. If a response is not received in apredefined period of time, the external communication device mayautomatically retransmit the message one or more times prior to alertingthe patient of a failure to communicate.

[0122] In the present embodiment, all transmissions both inbound andoutbound, and both solicited and unsolicited are sent using the samedata transmission rates and the same carrier frequency. In alternativeembodiments, however, data transmission rates may be varied, and carrierfrequency may be varied. Such variations may be based on predefined timeslot definitions so that both the implantable device and externalcommunication device may properly vary their reception parameters inanticipation of how the other device may attempt to communicate. Forexample, solicited transmissions may occur at a different carrier thanunsolicited transmissions or may occur using a different datatransmission rate. The external communication device may transmit oninbound time slots with a first carrier frequency and first data rate,and the implantable device may transmit on outbound time slots with asecond frequency or second data rate that may be different from thefirst frequency or first data rate. In still further embodiments,transmission reception & frequency may be user selectable ifcommunication problems are excessive in the hope of finding a frequencywith less interference.

[0123] To reduce power consumption, it is desirable to have telemetryhardware operate only during actual transmission times and duringpossible reception times and to have the CPU off for a large portion ofthe possible reception times and for a large portion of actualtransaction times. As such, the hardware, as discussed above, isconfigured and controlled so that this result is achieved. As powerconservation in the implantable device is more critical than powerconservation in the external communication device, this first embodimentplaces the burden associated with synchronization activities andactivities associated with reestablishing synchronization, once it islost, onto the external communication device. This desire to minimizepower drain in the implantable device is balanced with a desire to havethe implantable device respond quickly to commands transmitted by theexternal communication device. Once a command is issued by the externalcommunication device, it is preferred, for user/patient convenience,that the implantable device receive and acknowledge the command asquickly as possible. To this end, the implantable device is providedwith closely spaced reception slots (i.e. inbound listening intervals,e.g. every 2 seconds) so that communication can occur with asufficiently fast response. Each inbound listening period, however, isof very short duration so that power consumption in the implantabledevice is minimized.

[0124] The duration of each inbound listening period is preferably notso small that slight variations in synchronization cause lost ofreception, which would cause a delay in communication, as well aspotentially causing extra power consumption in order to reestablishcommunication as the reception hardware may be forced to remain on forextended periods of time due to the reception of lengthy attentionpreambles. As such, in the present embodiment the reception time slotsare turned on for an initial period of about 2-8 milliseconds (e.g. 4milliseconds) while using an 8 kHz data transmission rate with a minimumnumber of 8-bit transitions necessary for establishing bitsynchronization.

[0125] In alternative embodiments longer or shorter windows may be used.Relative to the incoming bit rate, it is preferred that the windowremain open in the range of about one and one-half to four times theperiod necessary to establish bit sync and receive a complete frame syncsignal.

[0126] In other alternative embodiments, if attention preamble is sent,the window may be opened only for a period necessary to establishreceipt of the attention preamble and thereafter, frame sync and a validtelemetry ID may be looked for. In this alternative, to enhancelikelihood of reception, the transmitter preferably does not begintransmission at what it believes is the most likely time that thereceiver begins listening, but instead begins transmission at a somewhatearlier time with an attention preamble of sufficient length to cover orat least sufficiently overlap the anticipated listening period.

[0127] In the present embodiment, the implantable device always starts atransmission exactly at (an outbound transmission start time whichcorresponds to a second boundary) according to its own clock. Theexternal communication device may activate its receiver at what itbelieves is the implantable device's outbound transmission start timebased on use of any synchronization parameters established inconjunction with the previous communication(s). The externalcommunication device may leave its reception window open for apredefined minimum period of time or alternatively it may adjust thelistening period based on one or more parameters. The receiver may useone or more additional parameters to adjust the opening of the receptionwindow to somewhat earlier than what it believes the actual start of thepotential transmission is to be. This early opening of the receptionwindow may be based on an anticipation that a certain amount ofincreasing uncertainty exists in the validity of the previouslyestablished synchronization and associated previously established driftparameters. In other words, this may be done in recognition that thereis a tolerance around which synchronization may be drifting. Suchadditional parameters may also be used to lengthen the reception windowbeyond a predefined initial listening period.

[0128] In this embodiment, the implantable device always turns on itsreceiver exactly at the beginning of an inbound reception time slot. Assuch, if the external communication device has a message to transmit tothe implantable device during that reception time slot, the externalcommunication device may start transmitting at what it believes is thebeginning of the time slot based on an estimated amount of drift thatmay have occurred. Alternatively, it may begin transmitting somewhatahead of its best estimate as to when the time slot will open, inanticipation that there is some degree of uncertainty in the actualamount of drift that has occurred between its measure of time and thatof the Implantable Device. In this regard, the external communicationdevice may use an extended preamble, possibly of the standard pattern ifnot extended too long, but more preferably of the attention pattern sothe chance of establishing communication is increased due to thereceiver's attribute of having its attention held (i.e. receptionhardware retained in an active state) by a communication that consistsof the attention preamble pattern. The parameter used in causing thewindow to open early may be a fixed parameter, or a parameter that isbased, at least in part, on the time difference between the present timeand the time of last establishing synchronization and possibly based onan estimate of maximum likely drift rate or based on an actual amount ofdrift experienced between the last two communications or between severalcommunication or associated with an amount or amounts of driftexperienced during approximately the same time periods during one ormore previous days. Similarly, the parameter used to extend the lengthof the standard preamble or attention preamble, or even to selectbetween them, may be a fixed parameter, a parameter that is based, atleast in part, on the time difference between the present time and thetime of last establishing synchronization or a parameter with adifferent basis.

[0129] If it is determined that resynchronization is needed, theexternal communication device may establish re-synchronization in one ofseveral ways. The external communication device may transmit a messagewith an extended preamble consisting of the attention preamble. Thisprocess may be done as a single step or it may be done in multiplesteps. In the single step process, the attention preamble is set to alength of time equal to or somewhat greater than the length of timebetween inbound listening intervals. This message is preferably a syncmessage as will be discussed hereafter though it may be also be adifferent message. After transmission of the message, the externalcommunication device leaves its receiver open for at least about 1-2seconds in anticipation of the implantable device sending an outboundresponse. The timing of the sync response message, as well as itscontent, will provide the information necessary to reestablishsynchronization.

[0130] The sync message is preferred over other messages because othermessages may not carry as much information about timing between theimplantable device and the external communication device as is carriedby the sync message. For example, all response messages may be used toreestablish synchronization of the second boundaries, but not allmessages necessarily carry sufficient information to reestablish evenversus odd second boundaries or information necessary to reestablishone-minute boundaries.

[0131] In one variation of this one step process, the externalcommunication device begins transmission of the message somewhat afterits best estimate (if it has one) as to when the reception window on theimplantable device will be closing. In this variation, it is hoped thatthe implantable device's receiver will open its reception window towardsthe end of transmission of the attention preamble, as opposed to towardthe beginning of transmission, so that power consumption by theimplantable device is minimized.

[0132] One potential multi-step process is similar to the one stepprocess discussed above, but the first one or more attempts to establishsynchronization use an attention preamble that is shorter than theinbound listening interval. In this regard, if the transmission catchesthe window, the receiver of the implantable device may be held open fora shorter period of time than that resulting from the one step processand thus a power savings in the implantable device may be achieved.However, if the transmission is not received, one or more subsequentmessages will need to be sent, with the associated inconvenience of anextra time delay. In this process, the first message is preferablycentered around the external communication device's best estimate as toinbound listening period. If communication and synchronization are notreestablished in response to the first message, one or more subsequentmessages may be transmitted with longer attention preambles that stillmay be shorter than the interval between inbound time slots, equal toit, or even greater than it. In any event, if communication andsynchronization are not reestablished using the previous attempts, afinal message will be sent with an attention preamble of length equal toor greater than the inbound listening interval. If communication hasn'tbeen reestablished based on transmitting attention preamble for a periodof time equal to or somewhat greater than the normal operation inboundlistening interval, it may be appropriate to send an attention preamblefor a time period equal to or somewhat greater than the storage modeinbound listening interval as the system may have inadvertently beenshifted to that mode. If communication is still not established, thepatient may be alerted to the problem so that he/she may reposition theexternal communication device relative to the implantable device, go toa different location where electromagnetic interference may be reduced,or otherwise seek assistance in addressing the problem.

[0133] As a second example of a potential multistep synchronizationprocess the length of the attention preamble may not be increased beyondthat selected for the first attempt, instead if multiple attempts areneeded, the start time of transmission may be shifted such that theentire set of messages, if required to be sent, will cover all possibleportions of the inbound listening interval by covering a differentportion of each interval in a series of intervals.

[0134] As a final alternative, if unsolicited communications areoutbound from the implantable device on a periodic basis, the externalcommunication device may simply open its reception window for the entireinterval between at least two of the successive periodic outboundcommunications so the message known to be transmitted sometime duringthe interval will be received if the devices are within telemetry rangeand other problems are not present thus enabling synchronization atleast in part reestablished.

[0135] As messages may have different levels of criticality, a higherlevel of error checking may be appropriate for some messages while alower level of error checking may be acceptable for other messages. Inthe present embodiment, all transmissions include some type of errorchecking or validation code where more critical messages are providedwith a more secure code. In the present embodiment, multiple levels ofsecurity have been defined. In particular, three levels of security havebeen established. In other embodiments fewer or greater numbers oflevels may be used. In the present embodiment, the three levels ofsecurity or criticality are known as (1) status, (2) command, and (3)critical. Status messages are the least critical and they aretransmitted with a 1-byte CRC code. Periodic status updates and responsemessages are examples of this message type. Command messages are ofintermediate criticality and are transmitted with a 16-bit CRC code.Critical messages are of the highest criticality and are subjected tothe highest level of security. These messages are used to establishinsulin delivery. Critical messages are transmitted with a 16-bit CRCand with duplicate data in the data portion of the message. The receiververifies that both copies of the data are identical before using themessage. Furthermore, various delivery amounts indicated in the messagesmay be compared to various predefined maximum amounts to confirm thatthey are within reasonable limits.

[0136] An example of an exception to the above preferred duplicating oftransmitted data, occurs with the set basal profile message whichtransmits 48 basal amounts for use during each of 48 half-hour periodsduring a day. Due to the length of this message, duplicate data is nottransmitted but the various basal rate amounts are compared to maximumbasal rate amounts programmed into the system.

[0137] In alternative embodiments, duplicate data transmission may beeliminated as an unnecessary precaution. Comparison of transmittedduplicate data can be more generally implemented or eliminated as anunnecessary precaution. In still further alternative embodiments,additional or other security precautions may be implemented such as, forexample, transmitting the desired data once but also transmitting aselected computed value that is derived from selected pieces of criticaldata that are intended to be in the message.

[0138] Some messages may be transmitted without expecting a response, inwhich case the sender will not know whether they were correctly received(non-response transactions). Other messages may require a response. If aresponse to these messages is not received, the transmitter will respondto the failure by repeating the transmission of the message. After apredefined number of transmission attempts without a response, themessage may be declared undeliverable, and the patient may be alerted tothe problem. In the present embodiment, outbound status messages do notrequire a response.

[0139] All messages (with the exception of the link message and theinterrogate message) that require a response and trigger an action inthe receiver, and all responses to such messages, are transmitted with asequence number. In the present embodiment, that sequence number is asingle bit that identifies the sequence of messages. As such, thissequence number is toggled between its two possible states “1” and “0”,by the transmitter each time a message is sent and the appropriateresponse (including the sequence number) is received. The receivertoggles its concept of what the sequence number should be when itreceives a valid message with the sequence number that it is nextexpecting. If it receives a message with a sequence number it is notexpecting, it sends a response indicating that the message was receivedbut does not act upon the content in the message. In alternativeembodiments, the sequence numbering may be removed or enhanced toinclude more than one bit. The sequence number is used to ensure that agiven message is only acted upon once, though the message may bereceived multiple times and multiple responses sent out. This situationmay occur when the sender does not receive the response and thenautomatically resends the message one or more times. The sender waitsfor a response with the appropriate sequence number and it disregardsany other responses with other sequence numbers. If a response is notreceived after one or more attempted retransmissions, thesynchronization process is attempted. If that fails, the patient isalerted to the condition so that subsequent steps may be taken. In anyevent, once communication is reestablished, the message is resent and anappropriate response looked for. If the original message was notreceived in the original transmission attempts, and was only received inthe last transmission attempt, and it dealt with an insulin deliveryissue that was not longer applicable, the delivery could be canceled bygoing into a suspend mode or by taking other steps in a timely manner.Suspend mode is an operational state of the implantable device whereinsulin delivery is reduced to a medically insignificant level.

[0140] If a received message requires a response, the recipient respondsduring the next available transmission period. If a received message hasan incorrect CRC, it is ignored. In the present embodiment, the senderof a messages waits a predetermined period of time for the anticipatedresponse message and if it does not receive the response as expected, ittakes the appropriate course of action as noted above.

[0141] In the present embodiment, software version numbers are includedwith software updates to allow upgradability of software functionalityand to ensure compatibility between external communication devices andtheir software versions and implantable devices and their softwareversions. A 2-byte version number is assigned to all versions of thetelemetry system. 1-byte is used for a telemetry version number and theother is for the telemetry revision number within that version.

[0142] Subsequent versions of the telemetry software are numbered suchthat when changes to the protocol create incompatibilities with earlierreleases, a new version number is used and the revision number is set tozero. When a new version of the telemetry software is compatible withprevious versions, the software version number is unchanged but therevision number is incremented. An application number may also beapplied to the software and checked for compatibility to avoid problemsassociated with mismatching of external communication devices andimplantable devices where the software in each may be designed fordifferent applications, such as delivering different types of drugs, foroperating with different units of measurement, or for controllingsystems with different hardware.

[0143] The user may need to change the time defined in the externalcommunication device. This may result from changes when travelingbetween time zones, due to annual shifts in time, as well as due toslight errors in tracking time. In the present embodiment, the externalcommunication device keeps track of minutes, hours, and days based onthe operation of its clock and any updates from a user. The externalcommunication device receives it concept of seconds within a minute fromthat found in the implantable device and as such does not allow userinput to update a second value. When the user changes the time on theexternal communication device, an appropriate message is transmitted tothe implantable device so that it may adapt to the new time of day. Thisis done because certain automatic delivery regimes (e.g. basal rateprofiles) are based on the time of day. In the present embodiment,delivery is not automatically changed between various days of the weekor month and as such the implantable device has no need of tracking thisinformation. However, if in alternative embodiments day sensitivedelivery routines are implemented in an automated manner then theexternal communication device could be programmed to pass thisinformation to the implantable device which may be programmed to acceptand use it. If it is found desirable for the communication device totrack seconds, in an alternative embodiment, the medical device couldobtain its concept of seconds from the communication device.

[0144] In some embodiments, software may be downloaded from the externalcommunication device to the implantable device. The downloading ofsoftware may include the downloading of executable software as well asthe downloading of data structures that may be used by the executablesoftware. This downloading of software may be only allowed to occur whenthe implantable device is in a no bootloader operation mode. Thebootloader operation mode is an intermediate operation state wherevarious communication activities can occur but where medicalfunctionality of the implantable device is inactivated or strictlylimited to a default mode of simplified operation. New software may beof the application type or of the bootloader type. In the presentembodiment, new application software is always loaded for both the mainand monitor processors at the same type. Replacement bootloader softwaremay be loaded for either processor individually. Application software isthe software that controls normal medical operation of the device alongwith telemetry operations when it is in control of the device.Bootloader software is the software that initially controls of thedevice immediately after start up and resetting. As such, in morepreferred embodiments, the software controlling the implantable devicewill allow certain communication operations to occur and will also alloweither the downloading of new software or the normal medical operationsof the device but not both simultaneously. In alternative embodiments,device operation may be modified so that application software may beloaded to either processor individually or so that downloading ofsoftware need not be limited to periods when the bootloader software isbeing executed.

[0145] The bootloader mode may be initiated in the implantable device bysending it a reset message from the external communication device.Downloading may be initiated by using a inbound load start message thatincludes an overall validation code (e.g. CRC) for the program that isto be downloaded (i.e. software image) along with its normal messagevalidation code (e.g. CRC) that is used to confirm that the startdownload message itself was properly received. The software may bedownloaded from a non-volatile memory module (e.g. a SEEPROM) in theexternal communication device, or from a second external device, thatholds implantable device software. Downloads then occur using one ormore inbound load continue messages each having data portions (excludingop-code and validation code). In the present embodiment, when loadingapplication software, the inbound load start and inbound load continuemessages are sent in series four times one for each of two images forthe main processor (one executable and one data) and for each of twoimages for the monitor processor (one executable and one data). Eachmessage that is sent carries its own validation code, that must beacknowledged as valid if the message is to be accepted and acknowledgedbefore additional messages are sent.

[0146] Once all program images have been downloaded, the new code isexecuted by transmitting a bootstrap message. A final validation code(e.g. CRC) for each program image that is supplied by the externalcommunication device is compared to a validation code (e.g. CRC) that isderived for each program image directly from the data that was received.For each calculated program image validation code that doesn't match thetransferred validation code, an error message is sent to the externalcommunication device and that program image is completely reloaded. Inany event, until all programs are confirmed to have been appropriatelyreceived, the implantable device remains in bootloader mode. Once eachcalculated validation code and each transmitted validation code matchfor each program image, the CPU is commanded to turn over control ofeach processor IC to its respective program. If the downloaded programsare replacement bootloader programs, once the validation codes (e.g.CRCs) are confirmed, the program images are copied over into theirpermanent positions within a non-volatile memory module and the deviceis reset so that upon reboot, the new bootloader code is executed.

[0147] In alternative embodiments, after each image is downloaded, acalculated validation code (e.g. CRC) may be compared to a transmittedvalidation code so that the program image may be confirmed as beingproperly received or be reloaded until it is properly received prior tocontinuing with the loading of any additional software images.

[0148] In alternative embodiments, instead of an overall CRC being sentfor each program, two overall CRCs may be sent where one is for themonitor processor IC images that were transmitted while the other is forthe main processor IC images that were transmitted. In still otherembodiments, a single overall CRC may be transmitted for all programsregardless of the processor IC on which they will be used.

[0149] The transmitted CRCs, the initially calculated CRCs (onceconfirmed to be correct), a CRC based on an initially configuredsoftware image (if not completely configured at the time of transfer),or other validation code may be retained by the implantable device andused to periodically confirm the continued proper configuration (i.e.that the software has not been corrupted) of the software images isretained and used by the implantable device.

[0150] In the present embodiment, a specific external communicationdevice is configured/programmed to communicate substantively with onlyone specific implantable device, that is in turn configured/programmedto communicate substantively with only the same specific externalcommunication device. An external communication device is capable ofretaining the telemetry ID of exactly one implantable device at a timeand an implantable device is capable of retaining the telemetry ID ofexactly one external communication device at a time. A small amount ofnon-substantive communication (i.e. communication that does not impactinsulin delivery) can occur between external communication devices andimplantable devices that are not linked (i.e. partnered or married) toone another (i.e. provided with each others telemetry IDs).

[0151] When it is necessary to link an external communication device toan implantable device, the following process may be carried out used.

[0152] (1) The linking process is initiated by an external communicationdevice sending an interrogate message. The interrogate message is sentusing the universal telemetry ID with a CRC code that is not based ontelemetry IDs. All implantable devices that are within telemetry rangereceive the message. The interrogate message transmits, among otherthings, an exclusion list that contains up to eight telemetry IDs ofimplantable devices to which the external communication device is not tobe linked. The first time that the interrogate message is sent outduring a given linking cycle, all eight IDs in the exclusion list areblank. All implantable devices that are within telemetry range and thatare not in the exclusion list respond to the interrogate command. Ifthere is more than one implantable device within telemetry range,multiple responses may be sent to the external communication device,however the external communication device will pick up only the first ofsuch responses. The response will contain personal ID information fromimplantable device. The personal ID of the implantable device containsuser identity information that was programmed into the implantabledevice. The personal ID of the implantable device is displayed on theexternal communication device display for verification by the user.

[0153] (2) The implantable device is then either accepted or rejected bythe user, based on the personal ID information that is provided. Theuser will reject the implantable device if the personal ID informationindicates that the wrong implantable device has responded. If theimplantable device is rejected, the telemetry ID of the implantabledevice is added to the exclusion list and the interrogate message isresent. This time the previously rejected implantable device will notrespond to the interrogate message. The process of rejecting implantabledevices may continue a plurality of times. If after the eighth attempt,a wrong implantable device is still responding to the interrogatemessage, the user must relocate himself/herself to a location away fromother implantable devices so that only the proper device will respond.

[0154] (3) Once the desired implantable device has responded, beenreceived, and is accepted, a link external communication device toimplantable device message is transmitted to the specific implantabledevice using its telemetry ID along with the telemetry ID of theexternal communication device.

[0155] (4) The implantable device responds to the link message, and theprocess is complete. The implantable device and external communicationdevice are now linked and may communicate substantive informationconcerning medication delivery based on their specific telemetry IDs(assuming the implantable device is operating in the normal applicationmode as opposed to the bootloader mode discussed above).

[0156] In the present embodiment, many different types of messages andresponses thereto can be written into the programs that control theimplantable device and the external communication device according tothe protocol features set forth above. These messages may be used for anumber of different purposes. For example, (1) they may be system levelmessages that are used for testing devices, for resetting devices, orfor establishing relationships between implantable devices and externalcommunication devices, (2) they may be alarm messages that are used toconvey alarm conditions or to clear alarm conditions, (3) they may bemiscellaneous messages that set various parameters or perform variousread operations, (4) they may be delivery messages that set deliveryamounts, read delivery status, or set parameters such as concentrationand pump stroke volume that may be required to appropriately controldelivery of the drug, (5) they may be data log messages that set datalog boundaries, read boundaries, or clear data logs, boundaries or readinformation from various data logs or supply information to those datalogs, (5) they may be refill messages that are related to amounts ofmaterial that are added to the reservoir periodically, (7) they may becompound messages that perform more than one function, or (8) they maybe error messages that request error condition status or supply errorcondition status. In other embodiments, messages may be classified indifferent ways. For illustrative purposes, examples of messages areprovided herein next.

EXAMPLE 1 System Level—Sync Message

[0157] This message may be sent when time synchronization between theexternal communication device and the implantable device has been lost.The sync response, like all messages, is sent starting on the secondboundary, so the subsecond information is implicitly transmitted aszeros. The sync message is sent by the external communication devicewith an attention preamble. When the external communication deviceattempts to transmit a message to the implantable device, and theexternal communication device does not receive a response, this messageis used to regain a communication link with the implantable device. Theduration of the attention preamble may be set as large as the listeninginterval during normal mode operation or it may be even increasedfurther if it is believed that the implantable device may have switchedinto storage mode. The message may be sent using (1) the specifictelemetry ID of the implantable device, (2) a 1-byte op-code without asequence number, and (3) a 16-bit CRC.

[0158] Once the sync message is transmitted by the externalcommunication device, it expects to the receive a response form theimplantable device. This response is in the form of a sync responsemessage. The sync response message is sent to the external communicationdevice with (1) a 1-byte sync response op-code (no sequence number), (2)a 1-byte value supplying the number of the half hour (0 to 47) of theday under which the implantable device is operating, (3) a 1-byte valueindicating the minute within the half hour (0 to 29), (4) a 1-byte valueof the second within the minute (0 to 59), (5)a 1-byte value indicatingthe next sequence number expected by the implantable device, and (6) a16-bit CRC. In other embodiments other information could passed with themessage, more information, or less information could be passed with themessage. For example, if the external communication device is only goingto update its concept of seconds within a minute based on the receipt ofthis response message, then the response could be limited to inclusionof only that data. On the other hand, if the external communicationdevice will compare the received minute and half hour values to itsconcept of those values and initiate a set current time message inreturn to update the implantable device's concept of time if necessarythen transmission of this extra information may be useful.Alternatively, such information may also be useful if the externalcommunication device will inform the patient of any discrepancy betweenthe concept of time on the two devices so that the patient can make adecision as to whether the time on the implantable device should beupdated to match that on the external communication device.

EXAMPLE 2 System Level—Reset Message

[0159] The reset message is used to force the implantable devicesoftware to enter bootloader mode (i.e. reload the bootloader software)and to thereby exit application mode (stop execution of applicationsoftware). This message may be sent out to prepare the implantabledevice to accept new software that can be supplied with inbound loadstart message, in conjunction with the inbound load continue messages,and then to restart the application software with a bootstrap command.In embodiments where the reset operation and the reloading of thebootloader software doesn't damage the application software previouslyloaded in the medical device, it may be possible to simply restart theapplication software using the bootstrap command without first reloadingit. This may be useful if for example, the reset operation was not doneso that new application software could be loaded for both processors butinstead was done so that new bootloader software could be loaded or sonew application software could be loaded for only one of the processors.This message is sent using (1) the telemetry ID of the implantabledevice, (2) a 7-bit op-code, (3) a 1-bit sequence number, and (4) a16-bit CRC. In the present embodiment, the implantable device does notsupply any response to the reset message.

EXAMPLE 3 System Level—Initiate Self-Test and Response

[0160] This message triggers the implantable device software to performself-test diagnostics. When the implantable device detects an error, theerror will be transmitted in the regular outbound message slot using anerror message. The response message indicates that the message wasreceived and that the tests were initiated. The self test message issent to the implantable device with (1) the implantable device'stelemetry ID, (2) a 7-bit op-code, (3) a 1-bit sequence number, and (4)a 16-bit CRC.

[0161] The response message is sent from the implantable device to theexternal communication device with (1) the telemetry ID of the externalcommunication device, (2) a 7-bit op-code, and (3) a 1-bit sequencenumber that corresponds to the sequence number of the original message.

EXAMPLE 4 System Level—Read Self-Test Progress

[0162] The Read Self-Test Progress message is used to determine thestatus of the previously requested self test. This message may beautomatically sent out by the external communication device (undersoftware control) on a periodic basis until a reply message is receivedindicating that the tests have been completed. This message is sent outwith (1) the telemetry ID of the implantable device, (2) a 7-bitop-code, (3) a 1-bit sequence number, and (4) a 16-bit CRC.

[0163] The response message is sent from the implantable device to theexternal communication device using (1) the telemetry ID of the externalcommunication device, (2) a 7-bit op-code, (3) a 1-bit sequence numbermatching the sequence number of the original message, (4) a 1-byte dataelement from which status information can be interpreted by the externalcommunication device, and (5) a 16-bit CRC.

EXAMPLE 5 System Level—Interrogate Message

[0164] The interrogate message is used to obtain identificationinformation from an implantable device. This command is used when theexternal communication device must learn the telemetry identification ofthe implantable device. The interrogate message initially uses anattention preamble equal to the normal mode inbound listening interval(e.g. 2 seconds). However, if there is no response, the externalcommunication device retries with an attention preamble having a lengthequal to the storage mode inbound listening interval (e.g. 15 seconds).If the telemetry ID of an implantable device is in the exclusion listfield of this message, that implantable device does not respond. Thismessage is sent with (1) the universal telemetry ID rather than thespecific telemetry ID of the implantable device, (2) a 1-byte op-code,(3) 3 bytes setting forth the telemetry ID of the external communicationdevice, (4) 24-bytes setting forth telemetry IDs of excluded implantabledevices, and (5) a 16-bit CRC.

[0165] The response to this message is sent to the externalcommunication device with (1) its specific telemetry ID, (2) a 7-bitop-code, (3) a 1-bit sequence number corresponding to the value expectedto be seen by the implantable device upon receipt of a next message thatcontains a sequence number, (4) a 1-byte bolus number indicative of thenext bolus number that the implantable device expects to see when itreceives a message that contains a bolus number, (5) 3 bytes settingforth the telemetry ID of the implantable device, (6) a 1-byteindication as to whether the implantable device is operating undercontrol of application software or bootloader software, (7) a 1-bytenumber indicating the application under which the implantable device isbeing used, (8) a 2-byte designation of the telemetry version andrevision number, (9) a 2-byte indication of the version and revision ofthe application software operating on the implantable device, (10) a32-byte personal identification field for the pump patient, (11) a4-byte bit field that indicates what alarms will be asserted (i.e.reasserted) by the implantable device, and (12) a 16-bit CRC.

EXAMPLE 6 System Level—Link Message

[0166] This message is used to associate an external communicationdevice and an implantable device. This message is sent following theinterrogate message and receipt of a response from the implantabledevice that is to be linked to. The link external communication deviceto implantable device message may be transmitted with an attentionpreamble equal to the normal mode inbound listening interval (e.g. 2seconds). However, if there is no response, the external communicationdevice retries with an attention preamble having a length equal to thestorage mode inbound listening interval. This message is sent with (1)the telemetry ID of the implantable device, (2) a 7-bit op-codeindicating that this is the link message, (3) a 1-bit sequence numberset to equal the sequence number obtained from the response to theinterrogate message, (4) 3 bytes of telemetry ID for the externalcommunication device, and (5) a 16-bit CRC that is not based on thetelemetry ID of the external communication device.

[0167] A response to the link message is sent from the implantabledevice back to the external communication device. The response to thismessage is sent with (1) the telemetry ID of the external communicationdevice, (2) a 7-bit op-code indicating that it is the response to a linkmessage, (3) a 1-bit sequence number corresponding to the value used inthe link message, (4) a 4-byte bit field that indicates what alarms willbe asserted (i.e. reasserted) by the implantable device, (5) a 1-bytevalue indicating the current half hour value since midnight, (6) a1-byte value indicating the current minute within the half hour, (7) a1-byte value indicating the current second within the minute, (8) a4-byte value indicating of the number of minutes since the implantabledevice was first initialized, and (9) a 16-bit CRC.

EXAMPLE 7 System Level—Bootstrap

[0168] The bootstrap message is used to confirm that the CRCs of thedownloaded software images are correct and then to cause both processorsof the implantable device to transfer control from the bootloadersoftware to the application software. If the calculated CRCs do notmatch the CRCs of the downloaded software, an error message is sent toindicate that there is an error, and the software remains in thebootloader mode. In some embodiments, this error may give rise toretransmission of all software images or only those that could not bevalidated. If the implantable device is operating under control of theapplication software when the bootloader message is received, themessage is acknowledged with the bootstrap response message, however,there is no mode change. This message is sent with (1) the telemetry IDof the implantable device, (2) a 7-bit op-code indicating that this isthe bootstrap message, (3) a 1-bit sequence number set to match the nextsequence number expected to be received by the implantable device, and(4) a 16-bit CRC.

[0169] The response message is sent with (1) the telemetry ID of theexternal communication device, (2) a 7-bit op-code indicating that thismessage is the response to the bootstrap message, (3) a 1-bit sequencenumber matching the sequence number of the bootstrap message, and (4) an8-bit CRC.

EXAMPLE 8 System Level—Inbound Load Start Message

[0170] The inbound load start message provides the means to initiate theload of the implantable device with application software. Theimplantable device must be running in the bootloader mode for thiscommand to have an effect. If the implantable device is in thebootloader mode, then the inbound load start message causes the inboundload start message data to be parsed and stored into the memorylocations specified by the load data field of the message. As thebootloader software expects to download a certain number of softwareimages (e.g. 4 images—1 software code image for the monitor processor, 1data image for the monitor processor, 1 software code image of the mainprocessor, and 1 software data image for the main processor), the use ofthe inbound load start message is repeated after each download untileach expected image has been downloaded. This message is sent with (1)the telemetry ID of the implantable device, (2) a 7-bit op-codeindicating that the message is the inbound load start message, (3) a1-bit sequence number matching the next sequence number expected by theimplantable device, (4) a 1-byte field indicating whether the softwareimage that will be sent is for the monitor processor or for the mainprocessor, (5) a 2-byte number designating the segment value for theaddress where the software image is to start loading, (6) a 2-bytenumber designating the offset of the address where the software image isto start loading, (7) a 16-bit CRC for the entire software image that isto be downloaded potentially using multiple inbound load continuemessages, (8) a 1-byte field indicating whether the image to bedownloaded is data or program code, (9) a 1-byte field indicating thedownload image number, and (10) a 16-bit CRC for the message.

[0171] The response to the inbound load start message is sent to theexternal communication device with (1) its telemetry ID, (2) a 7-bitop-code indicating that the message is the response to an inbound loadstart message, (3) a 1-bit sequence number matching the sequence numberused on the originating message, and (4) an 8-bit CRC.

EXAMPLE 9 System Level—Inbound Load Continue Message

[0172] The inbound load continue message is the means to load theimplantable device with application software. The implantable devicemust be running in bootloader mode for this command to have an effect.

[0173] If the implantable device is in the bootloader mode, then thefirst inbound load continue message following an inbound load startmessage causes the load data portion of the message to be stored intothe memory locations specified by the address bytes specified in themost recent inbound load start message. As the software is loaded, theaddress is updated by the implantable device such that subsequentinbound load continue messages have their data loaded in contiguousmemory. As the external communication device is aware of the number ofinbound load continue messages it will take to download the entireimage, the sending of successive messages is repeated the requirednumber of times after each message is confirmed to have been correctlyreceived. The sending of the same message is repeated until aconfirmation of its appropriate receipt is obtained or until the patientis informed of the problem so that further action may be taken. Thismessage is sent with (1) the telemetry ID of the implantable device, (2)a 7-bit op-code indicating that the message is the inbound load continuemessage, (3) a 1-bit sequence number matching the sequence number thatthe external communication device believes that the implantable deviceis expecting next, (4) a 2-byte data count field indicating how manybytes of data are following in the message, (5) the number of bytes ofthe binary image of the software being download that were indicated inthe data count field, and (6) a 16-bit CRC.

[0174] Once the data is loaded and the receipt of the message validated,the implantable device returns a response message. No response isreturned if the validation of the message is not confirmed, in whichcase the implantable device simply awaits the resending of the message.The response message is sent with (1) the telemetry ID of the externalcommunication device, (2) a 7-bit op-coded indicating that the messageis the response to an inbound load continue message, (3) a sequencenumber matching the sequence number specified in the inbound loadcontinue message, and (4) an 8-bit CRC for the message.

EXAMPLE 10 Alarm—Read Alarm Condition Message

[0175] This message requests the implantable device to return a responsemessage that indicates the alarm condition states of the implantabledevice. This message is sent from the external communication device tothe implantable device with (1) the telemetry ID of the implantabledevice, (2) a 7-bit op-code indicating that this is the read alarmcondition message, (3) a 1-bit sequence number providing the sequencenumber next expected by the implantable device, and (4) a 16-bit CRC.The response provides (1) the telemetry ID of the external communicationdevice, (2) a 7-bit op-code indicating that this message is a responseto a read alarm conditions message, (3) a 1-bit sequence number thatprovides the sequence number used in the read alarm conditions messagethat gave rise to the response, (4) a 4-byte field indicating thecurrent alarm state of the implantable device, (5) a 4-byte fieldindicating which alarms will be reasserted in the future, and (6) an8-bit CRC

EXAMPLE 11 Alarm—Clear Alarm Condition Message

[0176] This message clears an alarm condition in the implantable device.If there is more than one alarm condition in the implantable device,each alarm condition may be cleared individually. This message is sentwith (1) the telemetry ID of the implantable device, (2) a 7-bit op-codeindicating that this is the clear alarm condition message, (3) a 1-bitsequence number that is next expected by the implantable device, (4) a4-byte field indicating which alarm condition to clear, and (5) a 16-bitCRC. The response is sent with (1) the telemetry ID of the externalcommunication device, (2) a 7-bit op-code indicating that the message isa response to the clear alarm condition message, (3) a 1-bit sequencenumber providing the sequence number used with the original message, (4)a 4-byte field indicating remaining alarm conditions that have not beencleared, and (5) an 8-bit CRC.

EXAMPLE 12 Miscellaneous—Read Current Time

[0177] This message reads the time in the implantable device. Themessage sends (1) the telemetry ID of the implantable device, (2) a7-bit op-code indicating that the message is the read current timemessage, (3) a 1-bit sequence number providing the next sequence numberexpected the implantable device, and (4) a 16-bit CRC.

[0178] The response to this message is sent from the implantable deviceback to the external communication device. The response to this messageis sent with (1) the specific telemetry ID of the external communicationdevice and is sent with (2) a 7-bit op-code indicating that it is theresponse to a read current time message, (3) a 1-bit sequence numbercorresponding to the value used in the read current time message, (4) a1-byte value indicating the current half hour value since midnight, (5)a 1-byte value indicating the current minute within the half hour, (6) a1-byte value indicating the current second within the minute, (7) a4-byte value indicating the number of minutes since the implantabledevice was first initialized, and (9) an 8-bit CRC.

[0179]

EXAMPLE 13 Miscellaneous—Set Current Time

[0180] This message sets the time in the implantable device. Moreparticularly in the present embodiment, this message sets the half hournumber since midnight and the minute number within the half hour. Thismessage does not update the implantable device's concept of what thecurrent second is or its concept of how many minutes have lapsed sinceit was initialized. The primary result of this message is to synchronizethe basal rate that the implantable device is delivering as compared tois what the external communication device believes it should bedelivering. In the present embodiment, the implantable device changesthe time to the values specified in this message synchronous to thebeginning of the next minute. This message is sent from the externalcommunication device to the implantable device. It is sent to theimplantable device with (1) its specific telemetry ID, (2) a 7-bitop-code indicating that it is the set current time message, (3) a 1-bitsequence number providing the next sequence number expected by theimplantable device, (4) a 1 byte value indicating the current half hourvalue since midnight according to the external communication device, (5)a 1-byte value indicating the current minute within the half houraccording to the external communication device, and (6) a 16-bit CRC.

[0181] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a set current time message, (3) a 1-bitsequence number matching the sequence number of the set current timemessage, and (4) an 8-bit CRC.

[0182]

EXAMPLE 14 Miscellaneous—Read Personal ID Message

[0183] This message reads the current value of the personal IDinformation previously set into the implantable medical device. Thismessage is directed from the external communication device to theimplantable device. The message sends (1) the telemetry ID of theimplantable device, (2) a 7-bit op-code indicating that this is the readpersonal ID message, (3) a 1-bit sequence number providing the nextsequence number expected by the implantable device, and (4) a 16-bitCRC.

[0184] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a read personal ID message, (3) a 1-bitsequence number matching the sequence number of the read personal IDmessage, (4) a 32-byte field providing the personal ID information thatwas previously entered into the implantable device, and (5) an 8-bitCRC.

[0185]

EXAMPLE 15 Miscellaneous—Set Personal ID Message

[0186] This message sets the personal ID parameter for the implantabledevice to that which was entered into an implantable device personal IDfield in the external communication device. This message is directedfrom the external communication device to the implantable device. Themessage sends (1) the telemetry ID of the implantable device, (2) a7-bit op-code indicating that this is the set personal ID message, (3) a1-bit sequence number providing the next sequence number expected by theimplantable device, (4) a 32-byte field that contains the personal IDinformation for the implantable device that was previously entered intothe external communication device, and (5) a 16-bit CRC.

[0187] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a set personal ID message, (3) a 1-bit sequencenumber matching the sequence number of the set personal ID message, and(4) an 8-bit CRC.

[0188]

EXAMPLE 16 Miscellaneous—Memory Read Message

[0189] This message reads a portion of the memory in the implantabledevice that is requested by the user using the external communicationdevice. This message is directed from the external communication deviceto the implantable device. The message sends (1) the telemetry ID of theimplantable device, (2) a 7-bit op-code indicating that this is the readmemory message, (3) a 1-bit sequence number providing the next sequencenumber expected by the implantable device, (4) a 2-byte count valueindicating the number of bytes of memory to read, (5) a 2-byte valueindicating the offset of the memory address where reading is supposed toinitiate, (6) a 2-byte value indicating the segment of the memoryaddress where reading is supposed to initiate, (7) a 1-byte indicationas to whether the memory address is for the monitor or the mainprocessor, and (8) a 16-bit CRC.

[0190] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a read memory message, (3) a 1-bit sequencenumber matching the sequence number of the read memory message, (4) a2-byte count field indicating the number of bytes of the memory imagethat is being supplied plus the number of bytes in the CRC, (5) a memoryimage having the number of bytes indicated in the count field less two,and (6) a 16-bit CRC.

EXAMPLE 17 Insulin Delivery—Set Profile Rates

[0191] This message is used to set a basal rate profile amount to besupplied during each half hour of the day. As such this message is usedto set 48 different rates to be used in the delivery of basal rates ofinsulin. The 48 different rates are entered by the user into theexternal communication device either implicitly or explicitly. Theexternal communication device calculates basal rates in units of pumpstrokes per minute. The stroke volume and insulin concentration aretaken into account to ensure that a reasonable error tolerance is notexceeded. The implantable device compares each of the entries of theprofile table field to the maximum basal rate set by a set maximumsmessage. If any entry in the profile table is greater than the maximumbasal rate, the implantable device sends an error message to theexternal communication device. In an alternative embodiment, the messagecould be ignored by the implantable device, thus forcing the externalcommunication device to resend the message in order to receive itsexpected response.

[0192] The message sends the (1) telemetry ID of the implantable device,(2) a 7-bit op-code indicating that this is the set profile ratesmessage, (3) a 1-bit sequence number providing the next sequence numberexpected by the implantable device, (4) a 96-byte profile tableproviding a 2-byte value for each rate being supplied, and (5) a 16-bitCRC.

[0193] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a set profile rate message, (3) a 1-bitsequence number matching the sequence number of the set profile ratemessage, and (4) an 8-bit CRC.

EXAMPLE 18 Insulin Delivery—Read Profile Rates

[0194] This message causes the implantable device to return the 48 halfhour basal rates (i.e. basal rate profile) currently controlling basalrate delivery in the implantable device.

[0195] The message sends (1) the telemetry ID of the implantable device,(2) a 7-bit op-code indicating that this is the read basal rate profilemessage, (3) a 1-bit sequence number providing the next sequence numberexpected by the implantable device, and (4) a 16-bit CRC.

[0196] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a read basal rate profile message, (3) a 1-bitsequence number matching the sequence number of the read basal rateprofile message, (4) a 96-byte field providing the basal rates for eachhalf hour of the day, (5) a 1-byte pointer (0-47) that indicates whichof the 48 basal rate values is in use by the implantable device, and (6)a 16-bit CRC.

EXAMPLE 19 Insulin Delivery—Read Lifetime Total Delivered

[0197] This message causes the implantable device to return the totalnumber of pump strokes that have occurred since the implantable devicewas initialized during manufacturing. The message sends (1) thetelemetry ID of the implantable device, (2) a 7-bit op-code indicatingthat this is the read lifetime total message, (3) a 1-bit sequencenumber providing the next sequence number expected by the implantabledevice, and (4) a 16-bit CRC.

[0198] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a read lifetime total delivered message, (3) a1-bit sequence number matching the sequence number of the read life timetotal delivered message, (4) a 3-byte field providing the total numberof pump strokes delivered during the life of the implantable device, and(5) an 8-bit CRC.

EXAMPLE 20 Insulin Delivery—Set Temp Basal Rate

[0199] A temporary basal rate is enabled by this message. A temporarybasal rate may be used to replace the basal rate that would otherwise bedelivery as dictated by the current half hour and the basal rate profilediscussed above. The temporary basal rate is set as a delivery rate foruse during a specified time interval. A remaining duration of atemporary basal rate may be ascertained by using the read deliverystatus message as will be discussed hereafter. An ongoing temporarybasal rate can be canceled by using the set temp basal rate message andsetting the duration to zero.

[0200] After receipt of the message and confirmation of the CRC, theimplantable device verifies that several duplicate fields match: (1) theop-code field, indicating that this is the set temporary basal ratemessage matches the duplicate op-code field, (2) the sequence numberfield matches the sequence number duplicate field, (3) the temporarybasal rate amount field matches the temporary basal rate amountduplicate field, and (4) the temporary basal rate duration field matchesthe temporary basal rate duration duplicate field. If there is aduplicated field that does not match its original, the receiver respondswith an error message. The message sends (1) the telemetry ID of theimplantable device, (2) a 7-bit op-code indicating that this is the settemporary basal rate message, (3) a 1-bit sequence number providing thenext sequence number expected by the implantable device, (4) a 2-bytevalue indicating the temporary basal rate amount, (5) a 2-byte valuethat indicates the number of minutes that the temporary basal rate is torun, (6) a duplicate of element 2, (7) a duplicate of element 3, (8) aduplicate of element 4, (9) a duplicate of element 5, and (10) a 16-bitCRC.

[0201] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a set temporary basal rate message, (3) a 1-bitsequence number matching the sequence number of the set temporary basalrate message, and (4) an 8-bit CRC.

EXAMPLE 21 Insulin Delivery—Deliver Bolus Message

[0202] This message causes the implantable device to deliver a bolus. Abolus is an amount of insulin that is dispensed in addition to theinsulin rate that is being dispensed according to the basal rate profileor temporary basal rate. In a preferred implementation, the implantabledevice returns an error message when a bolus message is sent and thereis an immediate bolus in progress, a priming bolus in progress, adiagnostic rate in progress, the implantable device is in a minimumdelivery mode (i.e. suspend mode), or the implantable device is in anon-delivery mode (i.e. stop mode). According to a preferredimplementation two bolus types may be provided simultaneously: (1) animmediate bolus (i.e. phase 1 bolus) amount that is to be dispensed asquickly as possible, and (2) an extended bolus (i.e. phase 2 bolus)amount that is to be dispensed as a rate over a predefined period oftime. Before implementing the requested bolus, the implantable devicealso verifies that various duplicate fields within the message match:(1) the op-code field, indicating that the message is the deliver bolusmessage is the same as the duplicate op-code field, (2) the sequencenumber field is the same as the sequence number duplicate field, (3) thebolus number field is the same as the bolus number duplicate field, (4)the immediate bolus amount field is the same as the immediate bolusamount duplicate field, (5) the phase 2 bolus rate field is the same asthe phase 2 bolus rate duplicate field, and (6) the phase 2 bolusduration field is the same as the phase 2 bolus duration duplicatefield. If there is a duplicated field that does not match its original,the implantable device sends an error message to the externalcommunication device.

[0203] The message sends (1) the telemetry ID of the implantable device,(2) a 7-bit op-code indicating that this is the deliver bolus message,(3) a 1-bit sequence number providing the next sequence number expectedby the implantable device, (4) a 1-byte field supplying a bolus number,(5) a 1-byte value indicating a phase 1 bolus amount, (6) a 2-byte valueindicating a phase 2 bolus rate (this may have been entered intoexternal communication device as an amount that was converted to a rateprior to compiling the message), (7) a 1-byte value indicating thenumber of minutes over which the phase 2 bolus should be delivered, (8)a duplicate of element 2, (9) a duplicate of element 3, (10) a duplicateof element 4, (11) a duplicate of element 5, (12) a duplicate of element6, (13) a duplicate of element 7, and (14) a 16-bit CRC.

[0204] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a deliver bolus response message, (3) a 1-bitsequence number matching the sequence number of the deliver bolusmessage, (4) a 2-byte number indicating how many pump strokes weredelivered in the previous phase 1 bolus, (5) a 2-byte number indicatinghow many pump strokes were delivered in the previous phase 2 bolus, (6)a 1-byte number indicating the duration of the previous phase 2 bolus,and (7) an 8-bit CRC.

EXAMPLE 22 Insulin Delivery—Set Insulin Concentration

[0205] This message sets the insulin concentration for the implantabledevice. The delivery of insulin is not influenced by the existence ofthis parameter in the implantable device as the external communicationdevice determines the correct amounts to deliver based on the value ofthe insulin concentration stored therein and passes the delivery amountsto the implantable device in the form of the number of pump strokes. Assuch, the primary usefulness of this number existing in the implantabledevice is for permanent storage and retrieval in case the externalcommunication device is lost or otherwise replaced. Prior to acceptingthe value transferred with this message the implantable device verifiesthat the various duplicate fields match: (1) the op-code field,indicating this is the set insulin concentration message is the same asthe set insulin concentration duplicate field, (2) the sequence numberfield is the same as the sequence number duplicate field, and (3) theinsulin concentration field is the same as the insulin concentrationduplicate field. If there is a duplicated field that does not match itsoriginal, the implantable device sends an error message to the externalcommunication device.

[0206] The message sends (1) the telemetry ID of the implantable device,(2) a 7-bit op-code indicating that this is the set insulinconcentration message, (3) a 1-bit sequence number providing the nextsequence number expected by the implantable device, (4) a 1-byte fieldthat indicates the insulin concentration, (5) a duplicate of element 2,(6) a duplicate of element 3, (7) a duplicate of element 4, and (8) a16-bit CRC.

[0207] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a set insulin concentration message, (3) a1-bit sequence number matching the sequence number of the set insulinconcentration message, and (4) an 8-bit CRC.

EXAMPLE 23 Insulin Delivery—Read Insulin Concentration

[0208] This message causes the implantable device to return the insulinconcentration to the external communication device. Before acting on theresponse to this message the external communication device verifies thatvarious duplicate fields within the response message match: (1) theop-code field, indicating that the message is a response to a readinsulin concentration message, matches the duplicate op-code field, (2)the sequence number field is the same as the sequence number duplicatefield, and (3) the insulin concentration field is the same as theinsulin concentration duplicate field. If there is a duplicated fieldthat does not match its original, the external communication devicesends another read insulin concentration message.

[0209] This message is sent from the external communication device tothe implantable device. It is sent with (1) the telemetry ID of theimplantable device, (2) a 7-bit op-code indicating that it is the readinsulin concentration message, (3) a 1-bit sequence number matching nextsequence number expected by the implantable device, and (4) a 16-bitCRC.

[0210] A response to the message is sent from the implantable device tothe external communication device. The response message includes (1) thetelemetry ID of the external communication device, (2) a 7-bit op-codeindicating that it is the response to the read insulin concentrationmessage, (3) a 1-bit sequence number matching the sequence number of theread insulin concentration message, (4) a 1-byte field providing theconcentration of the insulin, (5) a duplicate of element 2, (6) aduplicate of element 3, (7) a duplicate of element 4, and (8) a 16-bitCRC.

EXAMPLE 24 Insulin Delivery—Read Maximums

[0211] This message causes the implantable device to return variousmaximum values associated with insulin delivery variables that arestored in the implantable device. Amounts received in telemetry messagesby the implantable device may be compared to these maximums as an addedsafety measure for ensuring that received messages were not corrupted orthe external communication device didn't act improperly. Beforeconsidering the response message to contain valid information, theexternal communication device verifies that several duplicate fields inthe response message match: (1) the op-code field, indicating that theresponse message is for a read maximums message, matches the duplicateop-code field, (2) the sequence number field matches the sequence numberduplicate field, (3) the maximum basal rate field matches the maximumbasal rate duplicate field, (4) the maximum bolus amount field matchesthe maximum bolus amount duplicate field, and (5) the maximum lock statefield matches the maximum lock states duplicate field. If a duplicatedfield does not match its original, the external communication deviceresends a read maximum message to the implantable device.

[0212] This message is sent from the external communication device tothe implantable device. It is sent with (1) the telemetry ID of theimplantable device, (2) a 7-bit op-code indicating that it is themaximums message, (3) a 1-bit sequence number matching next sequencenumber expected by the implantable device, and (4) a 16-bit CRC.

[0213] A response to the message is sent from the implantable device tothe external communication device. The response message includes (1) thetelemetry ID of the external communication device, (2) a 7-bit op-codeindicating that it is the response to the read maximums message, (3) a1-bit sequence number matching the sequence number of the read maximumsmessage, (4) a 2-byte value indicating a maximum acceptable value forany basal rate excluding a diagnostic rate, (5) a 1-byte valueindicating a maximum number of pump strokes that can be delivered in aphase 1bolus, (6) a 1-byte value indicating whether maximums can bechanged by the patient or whether a supervisor or physician password isrequired to change them, (7) a duplicate of element 2, (8) a duplicateof element 3, (9) a duplicate of element 4, (10) a duplicate of element5, (11) a duplicate of element 6 and (8) a 16-bit CRC.

EXAMPLE 25 Insulin Delivery—Set Maximums

[0214] The user interface for this message sets the delivery maximumswhile the message itself transfers them to the implantable device. Aswith most other delivery related messages various message fields areduplicated to enhance confidence that the received message has not beencorrupted. The implantable device verifies that duplicate fields in themessage match one another: (1) the op-code field, that indicates themessage is the set maximums message, matches the op-code duplicatefield, (2) the sequence number field matches the sequence numberduplicate field, (3) the maximum basal rate field matches the maximumbasal rate duplicate field, (4) the maximum bolus amount field matchesthe maximum bolus amount duplicate field, and (5) the maximum lock statefield matches the maximum lock states duplicate field. If there is aduplicated field that does not match its original, the implantabledevice reports and error back to the external communication device.

[0215] The message sends (1) the telemetry ID of the implantable device,(2) a 7-bit op-code indicating that this is the set maximums message,(3) a 1-bit sequence number providing the next sequence number expectedby the implantable device, (4) a 2-byte value that sets a maximumacceptable value for any basal rate excluding a diagnostic rate, (5) a1-byte value that sets a maximum number of pump strokes that can bedelivered in a phase 1 bolus, (6) a 1-byte value indicating whethermaximums can be changed by the patient or whether a supervisor orphysician password is required to change them, (7) a duplicate ofelement 2, (8) a duplicate of element 3, (9) a duplicate of element 4,(10) a duplicate of element 5, (11) a duplicate of element 6, and (12) a16-bit CRC.

[0216] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a set maximums message, (3) a 1-bit sequencenumber matching the sequence number of the set maximums message, and (4)an 8-bit CRC.

EXAMPLE 26 Insulin Delivery—Read Delivery Status

[0217] This message returns various values related to insulin delivery.The message sends (1) the telemetry ID of the implantable device, (2) a7-bit op-code indicating that this is the read delivery status message,(3) a 1-bit sequence number providing the next sequence number expectedby the implantable device, and (4) a 16-bit CRC. Unlike most otherinsulin delivery related messages this message does not includeduplicate fields.

[0218] The response to this message is sent from the implantable deviceto the external communication device. It is sent with (1) the telemetryID of the external communication device, (2) a 7-bit op-code indicatingthat it is a response to a read delivery status message, (3) a 1-bitsequence number matching the sequence number of the read delivery statusmessage, (4) a 2-byte value indicating the current basal rate value thatis being delivered, (5) a 1-byte profile index indicating the profilebasal rate that is running (unless the profile is overridden by adiagnostic rate or a temporary rate.), (6) a 2-byte value indicating anyremaining amount from an immediate bolus that is yet to be delivered,(7) a 1-byte value that indicates the number of minutes remaining untilcompletion of delivery of a phase 2 bolus, (8) a 2-byte value indicatingthe delivery rate of any phase 2 bolus that is in progress, (9) a 1-bytevalue indicating what the present delivery mode is (i.e. normal, suspendmode, stop mode, diagnostic rate delivery mode, priming bolus mode, orstorage mode), (10) remaining temporary basal rate duration, and (11) an8-bit CRC.

EXAMPLE 27 Insulin Delivery—Set Delivery Mode

[0219] This message is used to change the delivery mode of theimplantable device and to set certain delivery parameters. For addedsafety, the implantable device may limit what mode transitions arepossible. The implantable device and/or external communication devicemay be programmed to require a confirmation entry be made or message besent prior to actually making some mode transitions.

[0220] The implantable device verifies that several duplicate fieldswithin the message match prior to accepting the validity of the messageconveyed: (1) the op-code field, indicating that the message is the setdelivery mode message, is the same as the duplicate op-code field, (2)the sequence number field is the same as the sequence number duplicatefield, (3) the delivery mode field is the same as the delivery modeduplicate field, (4) the priming bolus amount field is the same as thepriming bolus amount duplicate field, and (5) the diagnostic rate fieldis the same as the diagnostic rate duplicate field. If there is aduplicated field that does not match its original, the implantabledevice sends an error message to the external communication device.

[0221] The message sends (1) the telemetry ID of the implantable device,(2) a 7-bit op-code indicating that this is the set delivery modemessage, (3) a 1-bit sequence number providing the next sequence numberexpected by the implantable device, (4) a 1-byte field that sets thedelivery mode to one of the normal mode, suspend mode, stop mode,diagnostic rate mode, priming bolus mode, or storage mode, (5) a 2-bytevalue that sets the number of pump strokes to be used when delivering apriming bolus, (6) a 2-byte value setting the diagnostic basal rate interms of a number of pump strokes per minute, (7) a duplicate of element2, (8) a duplicate of element 3, (9) a duplicate of element 4, (10) aduplicate of element 5, (11) a duplicate of element 6, and (12) a 16-bitCRC.

[0222] The response to this message is sent from the implantable deviceto the external communication. It is sent with (1) the telemetry ID ofthe external communication device, (2) a 7-bit op-code indicating thatit is a response to a set delivery mode message, (3) a 1-bit sequencenumber matching the sequence number of the set delivery mode message,and (4) an 8-bit CRC.

EXAMPLE 28 Refill—Set Refill Counter and Alarm Thresholds

[0223] This message is used to set various refill parameters. Themessage sends (1) the telemetry ID of the implantable device, (2) a7-bit op-code indicating that this is the set refill counter and alarmthreshold message, (3) a 1-bit sequence number providing the nextsequence number expected by the implantable device, (4) a 2-byte valuethat defines the number of pump strokes of medication that was added tothe reservoir after emptying it during the refill process, (5) a 2-bytevalue that defines the number of pump strokes of medication that remainin the reservoir when the low reservoir alarm is first triggered, (6) a2-byte value that defines the number of pump strokes of medication thatremain in the reservoir when the empty reservoir alarm is firsttriggered, and (7) a 16-bit CRC.

[0224] The response to this message is sent from the implantable deviceto the external communication. It is sent with (1) the telemetry ID ofthe external communication device, (2) a 7-bit op-code indicating thatit is a response to a set refill counter and alarm threshold message,(3) a 1-bit sequence number matching the sequence number of the setrefill counter and alarm threshold message, and (4) an 8-bit CRC.

EXAMPLE 29 Refill—Read Refill Counter and Alarm Thresholds

[0225] This message causes the implantable device to return currentvalues of various refill parameters. This message is sent from theexternal communication device to the implantable device. It is sent with(1) the telemetry ID of the implantable device, (2) a 7-bit op-codeindicating that it is read refill counter and alarm threshold message,(3) a 1-bit sequence number matching the next sequence number expectedby the implantable device, and (4) a 16-bit CRC.

[0226] The response to this message sends (1) the telemetry ID of theexternal communication device, (2) a 7-bit op-code indicating that thisis a response to the read refill counter and alarm threshold message,(3) a 1-bit sequence number providing the same sequence number as usedwith the originating message, (4) a 2-byte value that defines the numberof pump strokes of medication that was added to the reservoir during thelast refill process, (5) a 2-byte value that defines the number of pumpstrokes of medication that remain in the reservoir when the lowreservoir alarm is first triggered, (6) a 2-byte value that defines thenumber of pump strokes of medication that remain in the reservoir whenthe empty reservoir alarm is first triggered, (7) a 2-byte value thatindicates the remaining number of pump strokes of medication in thereservoir, and (8) a 16-bit CRC.

[0227] As illustrated by the above examples, the telemetry protocolelements of the present embodiment can be used to provide many differenttypes of messages that can be used in transferring software, commands,and information that is useful to the robust, effective, reliable, andsafe operation of an implantable medical device and more generically foran ambulatory medical device. It will be understood by those of skill inthe art that many other messages types may be defined and transferred.For example messages may be defined and transferred that relate to howdata logs are defined and read, how errors are communicated, and thelike.

[0228] While the above embodiment has primarily been concerned with animplantable infusion pump that dispenses insulin using a piston typepump mechanism, the telemetry protocol elements may be used in otherambulatory devices such as implantable pacemakers, defibrillators, otherimplantable tissue stimulators, implantable physiologic sensors such aselectrochemical oxygen sensors, peroxide sensors, or enzymatic sensorssuch as glucose sensors, externally carried infusion pumps, implantableinfusion pumps that use other pumping mechanisms or simply used excesspressure and controlled flow elements to infuse various medications anddrugs such as analgesics, drugs for treating AIDS, drugs for treatingpsychological disorders and the like. For example, the telemetryprotocol of the instant embodiment may be used with an external infusionpump that may or may not have a built in display and keypad but isequipped with a telemetry system that can communicate with a physicallyseparated communication device so that the pump need not be accessed inorder to provide commands to it and receive data from it.

[0229] In these various alternatives, the physical, electronic, andprogrammed features of the communication device and implantable devicemay have different components and features than presented above for theimplantable pump system so that their desired medical functionality andsafety requirements are achieved and such that appropriate control andfeedback is provided between the medical device and its communicationdevice.

[0230] In other alternative embodiments the medical device may includetwo medical devices such as an implantable pump and an implantablesensor. The pump may dispense a drug whose physiological impact on thebody (e.g. analgesic impact) is ascertained by the sensor oralternatively the sensor may supply a physiological reading thatindicates a need for infusion of the drug. The pump may operate in aclosed loop manner with the sensor or it may operate in an open loopmanner where the patient is required to interpret sensor outputinformation and is required to issue appropriate infusion commands tothe pump. For example, in the case of a diabetic patient, the drug maybe insulin and the sensor may detect glucose level.

[0231] In embodiments that include two implanted medical devices the twomedical devices may be implanted adjacent one another or at an extendeddistance from one another. If not placed in physical contact with oneanother, a lead may be used to provide power conduction from one deviceto the other and also be used to conduct communication signals betweenthe devices. Alternatively, each device may include at least onetelemetry system that allows direct communication between them or allowsindirect communication to occur via the external communication device orother external device. Each device may be supplied with its own powersupply. Depending on the communication requirements each device may usetwo way communication (i.e. both outbound and inbound communication) orallow only one way communication (i.e. outbound communication orpossibly inbound communication). Various telemetry systems may be used.For example, telemetry systems may be of the analog type, digital type,or mixed. They may be RF based, IR based, optically based, inductivelybased, acoustically based, have some other basis that allowscommunication signals to be transmitted safely through the body andpicked up by the receiver.

[0232] In other alternatives, both the medical device and thecommunication device may be external devices (e.g. an external pump andan external RF telemetry based communication device). In still furtheralternatives, a first type of medical device may be implanted (e.g. aninfusion pump or a sensor) while a second medical device may be external(e.g. the opposite of a sensor or an infusion pump). Where at least oneof the medical devices is external, it may also function as thecommunication device for the other medical device in which case it maypossess a display for providing information to the patient and a keypadfor allowing entry of commands for issuance to the implantable device aswell as for direct use by itself. Even if at least one of the medicaldevices is external, it may be inconvenient to access that device wheninformation is needed or commands must be given, as such an external,non-medical communication device may be supplied that has informationoutput (e.g. display) capabilities and input (e.g. keypad) capabilities.If a separate communication device is provided, the external medicaldevice may or may not have display and input capabilities.

[0233] The telemetry protocol elements of the present embodiment may beused with other forms of distant communication (e.g. between theimplantable device and other external devices or between the externalcommunication device and other external devices) via variouselectromagnetic links like IR, optical links, longer or shorterwavelength RF, audio links, ultrasonic links, and the like.

[0234] Various elements of the telemetry protocol may be used incombination or separately to enhance communications between ambulatorymedical devices and communication devices and/or controllers associatedtherewith.

[0235] In other embodiments two independent processors may be used thatoperate from a single timing chain. In these alternatives, it ispreferable that at least one of the timing signals (e.g. one of thelower frequency timers) be monitored by an independently timed watchdogcircuit to reduce the risk of timing problems going undetected.

[0236] In still additional embodiments, an implantable glucose sensormay be used in conjunction with an implantable insulin pump to providefeedback to the patient or physician on the effectiveness of the insulindelivery system. The patient could use the feedback to assist in makinginsulin delivery decisions in an open loop manner. Alternatively, theoperation of the pump could be tied to the sensor output in a more orless closed loop manner to give a more automated character to systemoperation. Insulin may be infused without any user intervention, withoutpre-delivery information, and even without direct post deliveryfeedback. In a less automated closed loop system, drug infusionrecommendations could be derived by the system and presented to the userbefore delivery or the system could require user acknowledgment prior toproceeding with delivery for amounts or rates exceed a predefined limit.The implantable sensor may have its own power supply or may receivepower from the control circuitry provided within the pump housingthrough a physical lead that connects them. Power may be suppliedthrough one or more independent leads or alternatively may betransferred over one or more data lines through the communicationsignals themselves. Communication may be exchanged in various waysincluding, for example, via galvanic leads, RF telemetry, fiber optics,and the like, and may be of digital, analog, or combined form. Thesensor system may include a plurality of sensor elements which mightallow continued glucose data to be supplied even though some portion ofthe sensors stop operating, lose calibration or produce questionablereadings. The most preferred sensors would include electronic processingcapability in the form of an integrated circuit mounted in or forming apart of a housing for the sensor. This configuration has the advantageof allowing digital communications between the physical sensor and anyseparated electronic control module.

[0237] Further teachings concerning implantable sensors and implantablesensor systems are found in a number of patents issued to D. A. Gough,including (1) U.S. Pat. No. 4,484,987, entitled “Method And MembraneApplicable To Implantable Sensor”; (2) U.S. Pat. No. 4,627,906, entitled“Electrochemical Sensor Having Improved Stability”; (3) U.S. Pat. No.4,671,288, entitled “Electrochemical Cell Sensor For ContinuousShort-Term Use In Tissues And Blood”; (4) U.S. Pat. No. 4,703,756,entitled “Complete Glucose Monitoring System With An ImplantableTelemetered Sensor Module”; and (5) U.S. Pat. No. 4,781,798, entitled“Transparent Multi-Oxygen Sensor Array And Method Of Using Same”. Eachof these patents is incorporated herein by reference as if set forth infull.

[0238] Still further teachings concerning implantable sensors and sensorsystems are found in a number of patents issued to J. H. Schulman, etal., including (1) U.S. Pat. No. 5,497,772, entitled “Glucose MonitoringSystem”; (2) U.S. Pat. No. 5,651,767, entitled “Replaceable CatheterSystem for Physiological Sensors, Stimulating Electrodes and/orImplantable Fluid Delivery Systems”(3) U.S. Pat. No. 5,750,926, entitled“Hermetically Sealed Electrical Feedthrough For Use With ImplantableElectronic Devices”(4) U.S. Pat. No. 6,043,437, entitled “AluminaInsulation for Coating Implantable Components and Other MicrominiatureDevices”; (5) U.S. Pat. No. 6,088,608, entitled “Implantable Sensor andIntegrity Test Therefor”; and (6) U.S. Pat. No. 6,119,028, entitled“Implantable Enzyme-Based Monitoring Systems Having Improved LongevityDue to Improved Exterior Surfaces”. Each of these patents isincorporated herein by reference as if set forth in full.

[0239] Additional further teachings concerning implantable sensors andsensor systems are found in (1) U.S. Pat. No. 5,917,346, issued to J. C.Gord, et al., and entitled “Low power current-to-frequency converter”;(2) U.S. Pat. No. 5,999,848, issued to J. C. Gord, and entitled “DaisyChainable Sensors for Implantation in Living Tissue”; (3) U.S. Pat. No.5,999,849, issued to L. D. Canfield, et al., and entitled “Low PowerRectifier Circuit for Implantable Medical Devices”; and (4) U.S. Pat.No. 6,081,736, issued to M. S. Colvin, et al., and entitled “ImplantableEnzyme-Based Monitoring Systems Adapted for Long Term Use”. Each ofthese patents is incorporated herein by reference as if set forth infull.

[0240] Further teachings concerning implantable infusion pumps are foundin a number of patents by R. E. Fischell, including (1) U.S. Pat. No.4,373,527, entitled “Implantable, Programmable Medication InfusionSystem”; (2) U.S. Pat. No. 4,494,950, entitled “Infusion Device Intendedfor Implantation in a Living Body”; (3) U.S. Pat. No. 4,525,165,entitled “Fluid Handling System for Medication Infusion System”(4) U.S.Pat. No. 4,573,994, entitled “Refillable Medication InfusionApparatus”(5) U.S. Pat. No. 4,594,058, entitled “Single Valve DiaphragmPump with Decreased Sensitivity to Ambient Conditions”(6) U.S. Pat. No.4,619,653, entitled “Apparatus For Detecting At Least One PredeterminedCondition And Providing An Informational Signal In Response Thereto In AMedication Infusion Systerrm”; (7) U.S. Pat. No. 4,661,097, entitled“Method for Clearing a Gas Bubble From a Positive Displacement PumpContained Within a Fluid Dispensing System”; (8) U.S. Pat. No.4,731,051, entitled “Programmable Control Means for Providing Safe andControlled Medication Infusion”and (9) U.S. Pat. No. 4,784,645,entitled, “Apparatus For Detecting A Condition Of A Medication InfusionSystem And Providing An Informational Signal In Response Thereto”. Eachof these patents is incorporated herein by reference as if set forth infull.

[0241] Still further teachings concerning infusion pumps are found in anumber of patents by Franetzki, including (1) U.S. Pat. No. 4,191,181,entitled “Apparatus For Infusion of Liquids”, (2) U.S. Pat. No.4,217,894, entitled “Apparatus for Supplying Medication to the Human orAnimal Body”(3) U.S. Pat. No. 4,270,532, entitled “Device for thePre-programmable Infusion of Liquids”(4) U.S. Pat. No.4,282,872,entitled “Device for the Pre-programmable Infusion of Liquids”U.S. Pat.No. 4,373,527, entitled “Implantable, Programmable Medication InfusionSystem”(5) U.S. Pat. No. 4,511,355, entitled “Plural Module MedicationDelivery System”(6) U.S. Pat. No. 4,559,037, entitled “Device for thePre-programmable Infusion of Liquids”(7) U.S. Pat. No. 4,776,842,entitled “Device for the Administration of Medications”. Each of thesepatents is incorporated herein by reference as if set forth in full.

[0242] Teachings concerning tissue stimulators are found in a number ofpatents by J. H. Schulman, including (1) U.S. Pat. No. 5,193,539,entitled “Implantable microstimulator”; (2) U.S. Pat. No. 5,193,540;entitled “Structure and Method of Manufacture of an ImplantableMicrostimulator”; and (3) U.S. Pat. No. 5,358,514, entitled “ImplantableMicrodevices with Self Attaching Electrodes”.Further teachings are alsofound in (1) U.S. Pat. No. 5,957,958, by Loeb et al., entitled“Implantable nerve or muscle stimulator e.g. a cochlear prosthesis”in(2) U.S. Pat. No. 5,571,148, by G. E. Loeb, et al., entitled“Implantable Multichannel Stimulator”; and in (3) PCT Publication No. WO00/74751, by A. E. Mann, and entitled “Method and Apparatus for InfusingLiquids Using a Chemical Reaction in an Implanted Infusion Device”. Eachof these publications is incorporated herein by reference as if setforth in full.

[0243] The control of an implantable sensor could be provided throughthe functionality of one or both Processor ICs. One Processor IC couldsupply power and/or control signals to the sensor(s) and receive databack from the sensor, while the other processor could monitor theactivity to ensure that sensor activity meets certain predefinedguidelines.

[0244] In other embodiments, the External Communication Device of thefirst embodiment could be functionally linked to an external glucosesensor system such as the continuous glucose monitoring system (CGMS)offered by Minimed Inc. of Northridge, Calif. The link may beestablished, for example, through a physical lead or by RF telemetry.

[0245] In other embodiments other implantable, or external, sensorsystems that measure something other than glucose could also befunctionally coupled to the implantable device either to receive powerand/or to provide data. Other such sensors might include oxygen sensors,peroxide sensors, pulse rate sensors, temperature sensors,accelerometers, and the like.

[0246] In still other alternative embodiments, the electronic controlsystem of the first embodiment could be configured to control one ormore implantable sensors or electrical stimulators with or withoutinfusion functionality incorporated into the implantable device.

[0247] Further embodiments will be apparent to those of skill in the artupon review of the disclosure provided herein. Still further embodimentsmay be derived from the teachings set forth explicitly herein incombination with the teachings found in the various patent applications.

[0248] While the description herein sets forth particular embodiments,it is believed that those of skill in the art will recognize manyvariations to the presented embodiments based on the teachings herein,as such it is believed that many additional modifications may be madewithout departing from the spirit of the teachings herein. Theaccompanying claims are intended to cover such modifications as wouldfall within the true scope and spirit of the present invention.

[0249] The disclosed embodiments are therefore to be considered asillustrative and not necessarily restrictive, the scope of the inventionbeing indicated by the appended claims, rather than the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

We claim,
 1. A medical system, comprising: a) an ambulatory medicaldevice (MD) comprising MD electronic control circuitry that furthercomprises at least one MD telemetry system and at least one MD processorthat controls, at least in part, operation of the MD telemetry systemand operation of the medical device, wherein the medical device isconfigured to provide a treatment to a body of a patient or to monitor aselected state of the body; and b) a communication device (CD)comprising CD electronic control circuitry that further comprises atleast one CD telemetry system and at least one CD processor thatcontrols, at least in part, operation of the CD telemetry system andoperation of the communication device, wherein the CD telemetry systemsends messages to or receives messages from the MD telemetry system,wherein a message is sent using one of a predefined plurality ofpreambles.
 2. The system of claim 1 wherein a first portion of the MDtelemetry system is incorporated into the MD processor and a secondportion of the MD telemetry system is external to the MD processor, orwherein a first portion of the CD telemetry system is incorporated intothe CD processor and a second portion of the CD telemetry system isexternal to the CD processor.
 3. The system of claim 2 wherein (1) theMD electronic control circuitry comprises at least one external MDfunctional module, other than the second portion of the MD telemetrysystem, that is external to the MD processor, (2) the CD electroniccontrol circuitry comprises at least one external CD functional module,other than the second portion of the CD telemetry system, that isexternal to the CD processor, (3) the MD processor comprises an internalMD CPU and at least one other internal MD functional module, or (4) theCD processor comprises an internal CD CPU and at least one otherinternal CD functional module.
 4. The system of claim 1 wherein themedical device comprises and implantable infusion pump for selectivelydispensing a drug.
 5. The system of claim 4 wherein the drug comprisesinsulin.
 6. The system of claim 1 wherein the medical device comprisesan implantable sensor for sensing a selected state of the body.
 7. Thesystem of claim 6 wherein the sensor comprises a glucose sensor.
 8. Thesystem of claim 1 wherein the medical device comprises an implantableelectrode for selectively stimulating a portion of the body of thepatient.
 9. The system of claim 1 wherein at least a portion of theplurality of preambles comprise different bit patterns.
 10. The systemof claim 9 wherein at least one bit pattern comprises a sequence thatincludes repeated use of a pattern of 10 or 01 and at least one otherbit pattern comprises a sequence that includes repeat use of a patternof 110, 011, 001, or
 100. 11. The system of claim 1 wherein at least aportion of the plurality of preambles comprise bit patterns of differentlengths.
 12. The system of claim 1 wherein a message is sent from thecommunication device to the medical device using a first preamble andwherein a message is sent form the medical device to the communicationdevice using a second preamble wherein the first and second preamblesare different.
 13. The system of claim 12 wherein the first preamblecomprises a sequence that includes repeated use of a pattern of 110 andwherein the second preamble comprises a sequence that includes repeateduse of a pattern of
 10. 14. The system of claim 12 wherein at least aportion of the preambles of messages sent to the medical device from thecommunication device have preambles of varying length.
 15. The system ofclaim 12 wherein the preambles of messages sent to the communicationdevice by the medical device have fixed lengths.
 16. The system of claim15 wherein at least some of the plurality of preambles comprise bothdifferent bit patterns and different lengths.
 17. The system of claim 1wherein a first preamble is used to send at least some messages from thecommunication device to the medical device and a second preamble, whichis different from the first preamble, is used to send at least somemessages from the medical device to the communication device.
 18. Thesystem of claim 1 wherein messages are sent from the communicationdevice to the medical device using at least two different preamblelengths.
 19. The system of claim 18 wherein a first preamble capturesand holds the attention of the MD telemetry system and as long as itcontinues to be received.
 20. The system of claim 18 wherein a secondpreamble is of a different pattern than the first preamble and does nothold the attention of the MD telemetry system beyond a prescribedinbound listening period.
 21. A medical system, comprising: a) anambulatory medical device (MD) comprising MD electronic controlcircuitry that further comprises at least one MD telemetry system and atleast one MD processor that controls, at least in part, operation of theMD telemetry system and operation of the medical device, wherein themedical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and b) acommunication device (CD) comprising CD electronic control circuitrythat further comprises at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein the MD telemetry system is configured toperform a bit pattern recognition that allows a selected level of faulttolerance in concluding that a selected portion of a message matches anexpected pattern to be received.
 22. The system of claim 21 wherein afirst portion of the MD telemetry system is incorporated into the MDprocessor and a second portion of the MD telemetry system is external tothe MD processor, or wherein a first portion of the CD telemetry systemis incorporated into the CD processor and a second portion of the CDtelemetry system is external to the CD processor.
 23. The system ofclaim 22 wherein (1) the MD electronic control circuitry comprises atleast one external MD functional module, other than the second portionof the MD telemetry system, that is external to the MD processor, (2)the CD electronic control circuitry comprises at least one external CDfunctional module, other than the second portion of the CD telemetrysystem, that is external to the CD processor, (3) the MD processorcomprises an internal MD CPU and at least one other internal MDfunctional module, or (4) the CD processor comprises an internal CD CPUand at least one other internal CD functional module. 24.The system ofclaim 21 wherein the bit pattern recognition and the fault toleranceanalysis is performed by hardware components.
 25. The system of claim 21wherein at least part of the bit recognition or fault tolerance analysisis performed via software that is being executed by a microprocessorthat is operating within the medical device.
 26. The system of claim 21wherein the selected portion of the message is a preamble that isintended to hold the attention of the MD telemetry system for a periodof time.
 27. The system of claim 26 wherein the period of time iscontrolled by the length of time that the preamble is being received bythe MD telemetry system.
 28. The system of claim 26 wherein the periodof time is about 24-bit times or more.
 29. The system of claim 28wherein the period of time is about 48-bit times or more.
 30. The systemof claim 28 wherein the period of time is about 96-bit times or more.31. The system of claim 21 wherein the fault tolerance is greater thanor equal to 1-bit out of 256-bits.
 32. The system of claim 31 whereinthe fault tolerance is greater than or equal to 1-bit out of 128-bits.33. The system of claim 32 wherein the fault tolerance is greater thanor equal to 1-bit out of 64-bits.
 34. The system of claim 21 wherein thefault tolerance is less than or equal to 32-bits out of 256-bits. 35.The system of claim 21 wherein the fault tolerance is less than or equalto 8-bits out of 128-bits.
 36. The system of claim 21 wherein the faulttolerance is less than or equal to 4-bits out of 64-bits.
 37. The systemof claim 21 wherein the fault tolerance is between 1 out of 64bits and 4out of 64-bits, inclusive.
 38. The system of claim 21 wherein themedical device comprises an implantable infusion pump for selectivelydispensing a drug.
 39. The system of claim 38 wherein the drug comprisesinsulin.
 40. The system of claim 21 wherein the medical device comprisesan implantable sensor for sensing a selected state of the body.
 41. Thesystem of claim 40 wherein the sensor comprises a glucose sensor. 42.The system of claim 21 wherein the medical device comprises animplantable electrode for selectively stimulating a portion of the bodyof the patient.